build: drop py3.9, hard pin pygfx on old deps, remove lockfile

[tlambert03]

ok, #234 got too complicated (too many things have changed, it's a much bigger update than I wanted). so this takes a different approach: just hard pin the deps that were in the lockfile, remove the lockfile

pygfx = ["pygfx==0.9.0", "rendercanvas ==2.0.1", "wgpu==0.19.3"]

we'll have to fix those other things later, in a dedicated pr

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.00%. Comparing base (d051c22) to head (ab35840).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #235      +/-   ##
==========================================
- Coverage   86.24%   86.00%   -0.25%     
==========================================
  Files          46       46              
  Lines        5228     5224       -4     
==========================================
- Hits         4509     4493      -16     
- Misses        719      731      +12     

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