feat(hugr-py): Allow providing visibility when building function definitions

[maximilianruesch]

Allows providing a visibility when constructing function definitions, for purposes of allowing annotation of these in guppylang.

Related to Quantinuum/guppylang#1482.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.80%. Comparing base (7890e2f) to head (6663248).
⚠️ Report is 10 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2862   +/-   ##
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  Coverage   83.80%   83.80%           
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  Files         267      267           
  Lines       53728    53728           
  Branches    47793    47793           
=======================================
  Hits        45029    45029           
  Misses       6284     6284           
  Partials     2415     2415           

Flag	Coverage Δ
python	88.50% <100.00%> (ø)

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[acl-cqc]

This looks much like what I put in as #2772 - sorry for lack of fanfare but can you check?

[maximilianruesch]

It is indeed the same / #2772 covers more (it allows to configure visibility of declarations, which I removed from this PR because private declarations are not really useful for me).

Closing this one, since it is redundant now.