fix(core): Harden grep fallback and parser detection

[mhiro2]

Summary

• Keep the editor responsive during the grep fallback by dispatching ripgrep asynchronously and
  scheduling the quickfix update on the main loop.
• Stop vimgrep-based fallback from descending into VCS metadata, dependency caches, and build
  outputs, and notify the user before the synchronous scan starts.
• Make PinWordSymbol honor its documented cword fallback when the buffer has no Treesitter
  parser registered.

Changes

• 7b1e516 : fix(symbol): guard parser detection so PinWordSymbol falls back to cword
  • Wrap vim.treesitter.get_parser in pcall so filetypes without a registered parser no
    longer raise out of has_parser, restoring the documented cword fallback path for
    PinWordSymbol.
  • Add regression tests covering the parser-missing case at both the has_parser and
    PinWordSymbol command levels.
• c4e2fac : fix(grep): harden fallback to keep the UI responsive on large projects
  • Run the ripgrep fallback through the callback form of vim.system and apply quickfix
    updates via vim.schedule, so large repositories no longer freeze the UI while results are
    gathered.
  • Notify the user before the synchronous vimgrep fallback runs and extend wildignore only
    for the duration of the call to skip common VCS, dependency, cache, and build directories.
  • Update and add tests to cover the new async dispatch shape, the scan-start notification,
    and the wildignore set/restore behavior.

[github-actions]

Benchmark Results

nvim --headless -u NONE -c "lua dofile('bench/run.lua')" -c "qa!"

== bench.bench_reapply ==
---------------------------------------------------------------------------------------------
Benchmark                                        Iters    Mean (us)     Min (us)     Max (us)
---------------------------------------------------------------------------------------------
reapply_all  slots=1 wins=1                         50          2.8          0.7         20.6
reapply_all  slots=1 wins=5                         50          6.2          3.4         21.0
reapply_all  slots=1 wins=10                        50         13.9          6.2         32.3
reapply_all  slots=1 wins=20                        50         13.7         12.2         42.0
reapply_all  slots=5 wins=1                         50          1.5          0.7         24.7
reapply_all  slots=5 wins=5                         50          6.2          4.1         10.6
reapply_all  slots=5 wins=10                        50         17.0          7.6         47.6
reapply_all  slots=5 wins=20                        50         17.9         14.2         43.6
reapply_all  slots=9 wins=1                         50          2.1          0.9         30.1
reapply_all  slots=9 wins=5                         50         12.2          5.0         42.5
reapply_all  slots=9 wins=10                        50          9.5          8.5         25.7
reapply_all  slots=9 wins=20                        50         26.4         16.4         80.8
---------------------------------------------------------------------------------------------

== bench.bench_apply ==
---------------------------------------------------------------------------------------------
Benchmark                                        Iters    Mean (us)     Min (us)     Max (us)
---------------------------------------------------------------------------------------------
apply_slot_globally  wins=1                        100          5.4          3.9         28.2
apply_slot_globally  wins=5                        100         19.7         18.8         37.5
apply_slot_globally  wins=10                       100         45.5         37.3        110.6
apply_slot_globally  wins=20                       100         84.3         75.5        166.6
apply_slot_for_window  existing=0                  200          4.4          3.7         30.3
apply_slot_for_window  existing=5                  200          6.8          4.2         46.0
apply_slot_for_window  existing=9                  200          5.2          4.6         29.4
---------------------------------------------------------------------------------------------

== bench.bench_clear ==
---------------------------------------------------------------------------------------------
Benchmark                                        Iters    Mean (us)     Min (us)     Max (us)
---------------------------------------------------------------------------------------------
clear_all_globally  slots=1 wins=1                  30         68.1         47.6        141.2
clear_all_globally  slots=1 wins=5                  30        185.7        135.5        383.8
clear_all_globally  slots=1 wins=10                 30        291.9        240.1        471.8
clear_all_globally  slots=5 wins=1                  30        118.2         78.0        213.5
clear_all_globally  slots=5 wins=5                  30        275.9        235.2        484.4
clear_all_globally  slots=5 wins=10                 30        521.2        447.2        803.3
clear_all_globally  slots=9 wins=1                  30        129.4         99.2        277.2
clear_all_globally  slots=9 wins=5                  30        391.4        341.3        670.1
clear_all_globally  slots=9 wins=10                 30        715.3        645.4       1013.5
---------------------------------------------------------------------------------------------

== bench.bench_set_clear ==
---------------------------------------------------------------------------------------------
Benchmark                                        Iters    Mean (us)     Min (us)     Max (us)
---------------------------------------------------------------------------------------------
set+clear cycle  wins=1                             50         26.7         13.5        209.3
set+clear cycle  wins=5                             50         38.9         36.0         59.6
set+clear cycle  wins=10                            50         75.2         67.2        122.5
---------------------------------------------------------------------------------------------

== bench.bench_jump ==---------------------------------------------------------------------------------------------
Benchmark                                        Iters    Mean (us)     Min (us)     Max (us)
---------------------------------------------------------------------------------------------
jump.next  slots=1                                 100         22.6          9.2         63.2
jump.next  slots=5                                 100       5104.6       4995.6       5669.4
jump.next  slots=9                                 100      15219.2      15031.4      16538.9
---------------------------------------------------------------------------------------------

== bench.bench_cword ==
---------------------------------------------------------------------------------------------
Benchmark                                        Iters    Mean (us)     Min (us)     Max (us)
---------------------------------------------------------------------------------------------
apply_cword_for_window                             200          2.7          2.1         50.1
---------------------------------------------------------------------------------------------

== bench.bench_symbol ==
---------------------------------------------------------------------------------------------
Benchmark                                        Iters    Mean (us)     Min (us)     Max (us)
---------------------------------------------------------------------------------------------
symbol: get_symbol (on identifier)                 200          8.5          4.4         83.8
symbol: get_symbol (on keyword)                    200         13.1          5.5         51.4
symbol: set+clear cycle (source=symbol)             50         23.7         17.1         83.2
symbol: set+clear cycle (source=cword)              50         15.6         13.1         45.9
---------------------------------------------------------------------------------------------

== SUMMARY ==
---------------------------------------------------------------------------------------------
Benchmark                                        Iters    Mean (us)     Min (us)     Max (us)
---------------------------------------------------------------------------------------------
reapply_all  slots=1 wins=1                         50          2.8          0.7         20.6
reapply_all  slots=1 wins=5                         50          6.2          3.4         21.0
reapply_all  slots=1 wins=10                        50         13.9          6.2         32.3
reapply_all  slots=1 wins=20                        50         13.7         12.2         42.0
reapply_all  slots=5 wins=1                         50          1.5          0.7         24.7
reapply_all  slots=5 wins=5                         50          6.2          4.1         10.6
reapply_all  slots=5 wins=10                        50         17.0          7.6         47.6
reapply_all  slots=5 wins=20                        50         17.9         14.2         43.6
reapply_all  slots=9 wins=1                         50          2.1          0.9         30.1
reapply_all  slots=9 wins=5                         50         12.2          5.0         42.5
reapply_all  slots=9 wins=10                        50          9.5          8.5         25.7
reapply_all  slots=9 wins=20                        50         26.4         16.4         80.8
apply_slot_globally  wins=1                        100          5.4          3.9         28.2
apply_slot_globally  wins=5                        100         19.7         18.8         37.5
apply_slot_globally  wins=10                       100         45.5         37.3        110.6
apply_slot_globally  wins=20                       100         84.3         75.5        166.6
apply_slot_for_window  existing=0                  200          4.4          3.7         30.3
apply_slot_for_window  existing=5                  200          6.8          4.2         46.0
apply_slot_for_window  existing=9                  200          5.2          4.6         29.4
clear_all_globally  slots=1 wins=1                  30         68.1         47.6        141.2
clear_all_globally  slots=1 wins=5                  30        185.7        135.5        383.8
clear_all_globally  slots=1 wins=10                 30        291.9        240.1        471.8
clear_all_globally  slots=5 wins=1                  30        118.2         78.0        213.5
clear_all_globally  slots=5 wins=5                  30        275.9        235.2        484.4
clear_all_globally  slots=5 wins=10                 30        521.2        447.2        803.3
clear_all_globally  slots=9 wins=1                  30        129.4         99.2        277.2
clear_all_globally  slots=9 wins=5                  30        391.4        341.3        670.1
clear_all_globally  slots=9 wins=10                 30        715.3        645.4       1013.5
set+clear cycle  wins=1                             50         26.7         13.5        209.3
set+clear cycle  wins=5                             50         38.9         36.0         59.6
set+clear cycle  wins=10                            50         75.2         67.2        122.5
jump.next  slots=1                                 100         22.6          9.2         63.2
jump.next  slots=5                                 100       5104.6       4995.6       5669.4
jump.next  slots=9                                 100      15219.2      15031.4      16538.9
apply_cword_for_window                             200          2.7          2.1         50.1
symbol: get_symbol (on identifier)                 200          8.5          4.4         83.8
symbol: get_symbol (on keyword)                    200         13.1          5.5         51.4
symbol: set+clear cycle (source=symbol)             50         23.7         17.1         83.2
symbol: set+clear cycle (source=cword)              50         15.6         13.1         45.9
---------------------------------------------------------------------------------------------