Fix: Validate SphereShape radius to prevent assertion failures (DART 6.16)

[jslee02]

Summary

• Replace DART_ASSERT(radius > 0.0) with proper validation using std::isfinite() and DART_WARN()
• Invalid values (NaN, infinity, non-positive) are now rejected with a warning instead of crashing
• Add unit tests covering all validation cases

Motivation

Addresses gz-physics#843 where DART crashes with an assertion failure when SphereShape::setRadius() receives invalid radius values from upstream physics interfaces.

Changes

• dart/dynamics/SphereShape.cpp: Added validation with graceful rejection
• tests/unit/dynamics/test_SphereShape.cpp: New test file with 5 test cases
• tests/unit/dynamics/CMakeLists.txt: New CMake config for dynamics tests
• tests/unit/CMakeLists.txt: Added dynamics subdirectory
• CHANGELOG.md: Added entry under DART 6.16.5

Testing

• Unit tests verify valid radius acceptance and invalid value rejection (NaN, Inf, zero, negative)
• Follows existing validation pattern from World::setTimeStep()

[chatgpt-codex-connector]

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Reviewed commit: ef60a68990

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[jslee02]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Swish!

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 58.81%. Comparing base (991315e) to head (9cec639).
⚠️ Report is 6 commits behind head on release-6.16.

Additional details and impacted files

@@               Coverage Diff                @@
##           release-6.16    #2441      +/-   ##
================================================
+ Coverage         58.74%   58.81%   +0.07%     
================================================
  Files               385      385              
  Lines             32194    32201       +7     
  Branches           3884     3888       +4     
================================================
+ Hits              18911    18939      +28     
+ Misses            13283    13262      -21     

Flag	Coverage Δ
unittests	58.81% <100.00%> (+0.07%)	⬆️

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

Files with missing lines	Coverage Δ
dart/dynamics/SphereShape.cpp	75.67% <100.00%> (+1.38%)	⬆️

... and 4 files with indirect coverage changes

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[jslee02]

@codex review

This PR branch is up to date with release-6.16. The validation approach using DART_WARN with fallback to default value is appropriate for this use case (handling invalid radius values from upstream physics interfaces like gz-physics).

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. You're on a roll.

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