Handle MetaSkeleton subscriptions in CollisionGroup

[jslee02]

• allow CollisionGroup to subscribe to any MetaSkeleton by deriving a version tag and tracking lifetime safely
• add an integration test covering MetaSkeleton (Group) subscription membership changes and collisions
• fix cross-platform transform initialization and casting for the new test

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• Run pixi run test-all to lint, build, and test your changes
• Add unit tests for new functionality
• Document new methods and classes
• Add Python bindings (dartpy) if applicable

[codecov]

Codecov Report

❌ Patch coverage is 95.65217% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 61.82%. Comparing base (e29c616) to head (df6b58b).
⚠️ Report is 234 commits behind head on main.

Files with missing lines	Patch %	Lines
dart/collision/CollisionGroup.cpp	94.11%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2277      +/-   ##
==========================================
+ Coverage   61.68%   61.82%   +0.13%     
==========================================
  Files         360      360              
  Lines       32580    32592      +12     
  Branches     4280     4285       +5     
==========================================
+ Hits        20098    20150      +52     
+ Misses      12482    12442      -40     

Flag	Coverage Δ
unittests	61.82% <95.65%> (+0.13%)	⬆️

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

Files with missing lines	Coverage Δ
dart/collision/CollisionGroup.hpp	100.00% <ø> (ø)
dart/collision/detail/CollisionGroup.hpp	100.00% <100.00%> (ø)
dart/collision/CollisionGroup.cpp	85.40% <94.11%> (+0.65%)	⬆️

... and 5 files with indirect coverage changes

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