Unregister collision detectors when the darstim plugin is unloaded

[azeey]

🦟 Bug fix

Partial fix for #442

Summary

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)
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[azeey]

Monterey build:

[codecov]

Codecov Report

Merging #529 (0b824ab) into gz-physics6 (871bab7) will increase coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head 0b824ab differs from pull request most recent head b10917a. Consider uploading reports for the commit b10917a to get more accurate results

@@             Coverage Diff              @@
##           gz-physics6     #529   +/-   ##
============================================
  Coverage        76.18%   76.19%           
============================================
  Files              142      142           
  Lines             7251     7254    +3     
============================================
+ Hits              5524     5527    +3     
  Misses            1727     1727           

Files Changed	Coverage Δ
dartsim/src/plugin.cc	100.00% <100.00%> (ø)

[scpeters]

Monterey build:

there is still one failing test in this build, but it did fix the UNIT_FindFeatures and INTEGRATION_DoublePendulum test failures, so this is definitely an improvement

[scpeters]

Monterey build:

there is still one failing test in this build, but it did fix the UNIT_FindFeatures and INTEGRATION_DoublePendulum test failures, so this is definitely an improvement

the COMMON_TEST_joint_features_bullet-featherstone test is now seg-faulting in JointFeaturesAttachDetachTest/0.JointAttachDetachSpawnedModel. I collected a backtrace implicating the btCollisionWorld destructor with EXEC_BAD_ACCESS. I will post the backtrace in #442.

[azeey]

Yes, the segfaults in bullet-featherstone are a separate problem. This is not meant to fix that. I'll update the description to say it partially fixes #442.

BTW, I believe the segfaults in bullet-featherstone are due to the order of destruction of unique_ptrs in Base.hh. Bullet seems to have a lot of interdependencies, so deleting objects in the right order is tricky. I have been able to reproduce the problem on linux when running under Valgrind, but I haven't had the chance to fix the issue.