Citadel: backport fix for dartsim segfaults

[scpeters]

🦟 Bug fix

Backport #529 to Citadel to fix #442 (gz-sim6 segfaults on macOS) on Citadel and gazebosim/gz-sim#2204

Summary

See #529 and #442 for context.

Original commit message:

Unregister collision detectors when the darstim plugin is unloaded (#529)

Fixes a segfault that occurs due to destructors being removed from memory before they're called

Checklist

• Signed all commits for DCO
• Added tests
• 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

Note to maintainers: Remember to use Rebase-and-Merge.

[mjcarroll]

Focal build is sad:

  [ 53%] Building CXX object dartsim/CMakeFiles/ignition-physics2-dartsim-plugin.dir/src/plugin.cc.o
  /github/workspace/dartsim/src/plugin.cc: In destructor 'ignition::physics::dartsim::{anonymous}::UnregisterCollisionDetectors::~UnregisterCollisionDetectors()':
  /github/workspace/dartsim/src/plugin.cc:78:22: error: 'dart::collision::CollisionDetector' has not been declared
     78 |     dart::collision::CollisionDetector::getFactory()->unregisterAllCreators();
        |     

[scpeters]

there are issues with the dart version in some CI builds

[scpeters]

actually it appears that dartsim isn't even found by the macOS CI. something in the logic for detecting the [email protected] formula must have changed...

[scpeters]

actually it appears that dartsim isn't even found by the macOS CI. something in the logic for detecting the [email protected] formula must have changed...

I believe the behavior changed after Homebrew/brew#15607