Add per-DoF mimic actuator mode

[jslee02]

• add per-DoF mimic actuator configuration and update mimic constraint handling
• guard coupler constraints for partial/mixed mimic joints to avoid null derefs; fall back to mimic motors otherwise
• surface gz-physics FAKE_INSTALL build logs when the nested build fails to ease CI debugging

Closes #1684.

API changes (with example)

Before (joint-wide mimic only):

joint->setActuatorType(dynamics::Joint::MIMIC);
joint->setMimicJoint(reference);
joint->setMimicMultiplier(2.0);
joint->setMimicOffset(0.1);

After (per-DoF mimic configuration):

joint->setActuatorType(1, dynamics::Joint::MIMIC);
dynamics::MimicDofProperties props;
props.mReferenceJoint = reference;
props.mReferenceDofIndex = 0;
props.mMultiplier = 2.0;
props.mOffset = 0.1;
joint->setMimicDofProperties({props});

Coupler constraints now activate only when every DoF is mimic with a valid reference; mixed joints fall back to mimic motors.

---

Before creating a pull request

• 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 62.28070% with 86 lines in your changes missing coverage. Please review.
✅ Project coverage is 61.31%. Comparing base (67c78d2) to head (db8b333).

Files with missing lines	Patch %	Lines
dart/dynamics/Joint.cpp	44.76%	58 Missing ⚠️
dart/dynamics/detail/GenericJoint.hpp	70.68%	17 Missing ⚠️
dart/dynamics/Skeleton.cpp	53.84%	6 Missing ⚠️
dart/constraint/CouplerConstraint.cpp	80.00%	3 Missing ⚠️
dart/constraint/ConstraintSolver.cpp	91.30%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2222      +/-   ##
==========================================
+ Coverage   61.27%   61.31%   +0.04%     
==========================================
  Files         352      352              
  Lines       31557    31641      +84     
  Branches     4084     4124      +40     
==========================================
+ Hits        19336    19401      +65     
- Misses      12220    12240      +20     
+ Partials        1        0       -1     

Flag	Coverage Δ
unittests	61.31% <62.28%> (+0.04%)	⬆️

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

Files with missing lines	Coverage Δ
dart/constraint/JointConstraint.cpp	79.38% <100.00%> (+0.18%)	⬆️
dart/constraint/MimicMotorConstraint.cpp	86.36% <100.00%> (+4.91%)	⬆️
dart/dynamics/Joint.hpp	100.00% <ø> (ø)
dart/dynamics/detail/JointAspect.hpp	100.00% <ø> (ø)
dart/constraint/ConstraintSolver.cpp	80.06% <91.30%> (+0.44%)	⬆️
dart/constraint/CouplerConstraint.cpp	76.34% <80.00%> (-0.23%)	⬇️
dart/dynamics/Skeleton.cpp	76.48% <53.84%> (-0.06%)	⬇️
dart/dynamics/detail/GenericJoint.hpp	78.98% <70.68%> (+3.28%)	⬆️
dart/dynamics/Joint.cpp	66.37% <44.76%> (-10.21%)	⬇️

... and 2 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[jslee02]

@codex review

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".