[tpe] Add DetachableJoint support

[Xinyu-Sheng]

🎉 New feature

Summary

This PR adds DetachableJoint feature support to the TPE (Trivial Physics Engine) plugin, enabling dynamic attachment and detachment of fixed joints between entities.

Fixes

Closes #818

Changes:

TPE Plugin (tpe/plugin/):

Base.hh: Add JointInfo struct and joints map for joint tracking
JointFeatures.hh/cc: Implement AttachFixedJointFeature, DetachJointFeature, SetJointTransformFromParentFeature with stub implementations for required joint interface methods
SimulationFeatures.cc: Add fixed joint constraint enforcement in WorldForwardStep (required for kinematic engines that lack built-in constraint solvers)
KinematicsFeatures.hh: Add FreeGroupFrameSemantics to feature list
plugin.cc: Include JointFeatures in plugin feature list
CMakeLists.txt: Add JointFeatures.cc to source files

Test (test/common_test/):

detachable_joint.cc: Update test to support kinematic engines that don't have gravity simulation

Background:

TPE is a kinematic physics engine without a built-in constraint solver. Unlike dynamic engines (Dartsim, Bullet), TPE requires manual enforcement of fixed joint constraints during each simulation step. This implementation maintains the relative pose between attached entities by recalculating child poses based on parent poses after each WorldForwardStep.

Test it

# Build with tests enabled
colcon build --packages-select gz-physics7 --merge-install --cmake-args -DBUILD_TESTING=ON

# Run detachable joint tests
cd build/gz-physics7
ctest -R "COMMON_TEST_detachable_joint" --output-on-failure## Checklist

Expected: All tests pass for bullet, bullet-featherstone, dartsim, and tpe.
Checklist

• Signed all commits for DCO
• Added tests
• Added example and/or tutorial
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

Backport Request

Please backport this change to:

• gz-physics8
• gz-physics7

Why this should be backported:

• Does not break API/ABI
• Enables TPE's attach/detach joint feature in older Gazebo versions, which is useful for pick-and-place tasks in frameworks like Open-RMF
• Minimal changes, low risk
• Implementation is compatible with older versions

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by and Generated-by messages.