Stabilize FCL contact normals and collision ordering

[jslee02]

Summary

• make FCL collision object keys deterministic and use them to keep contact ordering and normals consistent across clones and runs
• ensure collision object user data is preserved after refresh to avoid missed collisions when shapes update
• add regression coverage for collision ordering and FCL refresh behavior

Fixes #1425.

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[codecov]

Codecov Report

❌ Patch coverage is 96.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 61.86%. Comparing base (57064be) to head (c890687).

Files with missing lines	Patch %	Lines
dart/collision/fcl/FCLCollisionDetector.cpp	94.44%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2282      +/-   ##
==========================================
+ Coverage   61.82%   61.86%   +0.04%     
==========================================
  Files         360      361       +1     
  Lines       32592    32633      +41     
  Branches     4283     4292       +9     
==========================================
+ Hits        20149    20188      +39     
- Misses      12443    12445       +2     

Flag	Coverage Δ
unittests	61.86% <96.00%> (+0.04%)	⬆️

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

Files with missing lines	Coverage Δ
dart/collision/fcl/FCLCollisionObject.cpp	95.00% <100.00%> (+2.14%)	⬆️
dart/collision/fcl/FCLCollisionObject.hpp	100.00% <100.00%> (ø)
dart/collision/fcl/FCLCollisionDetector.cpp	87.24% <94.44%> (+0.22%)	⬆️

... and 4 files with indirect coverage changes

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