Add raycast filter option

[jslee02]

Describe your changes here.

• add optional filter callback to RaycastOption and expose via dartpy stubs
• apply filter handling in Bullet raycasts (all-hits when filtering, drop disallowed hits, keep closest when only one needed)
• add Bullet-only raycast filter unit coverage

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Before creating a pull request

• Run pixi run test-all to lint, build, and test your changes (failed locally due to Bullet double-precision linkage; rely on CI)
• Add unit tests for new functionality
• Document new methods and classes
• Add Python bindings (dartpy) if applicable

[codecov]

Codecov Report

❌ Patch coverage is 0% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 61.80%. Comparing base (992f7a2) to head (e30faa6).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
dart/collision/RaycastOption.cpp	0.00%	9 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2279      +/-   ##
==========================================
- Coverage   61.82%   61.80%   -0.02%     
==========================================
  Files         360      360              
  Lines       32592    32599       +7     
  Branches     4284     4285       +1     
==========================================
  Hits        20149    20149              
- Misses      12443    12450       +7     

Flag	Coverage Δ
unittests	61.80% <0.00%> (-0.02%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
dart/collision/RaycastOption.cpp	0.00% <0.00%> (ø)

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