Support setting solver iterations

[iche033]

🎉 New feature

Summary

Extends Solver feature to support setting solver iterations per step.

Added support in:

• dart: only applicable if solver type is PgsBoxedLcpSolver
• bullet-featherstone: sets solver iteration for btMultiBodyMCLPConstraintSolver. By default it's now set to 50 (same as the default value in //world/physics/bullet/solver/iters). Originally it was only 10. Changing to 50 improves stability and prevents objects from drifting.

Test it

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

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

[codecov]

Codecov Report

Attention: Patch coverage is 88.88889% with 7 lines in your changes are missing coverage. Please review.

Project coverage is 78.40%. Comparing base (492b124) to head (adc1b3d).

Files	Patch %	Lines
dartsim/src/WorldFeatures.cc	83.78%	6 Missing ⚠️
bullet-featherstone/src/WorldFeatures.cc	94.44%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #609      +/-   ##
==========================================
+ Coverage   78.32%   78.40%   +0.08%     
==========================================
  Files         140      140              
  Lines        8069     8132      +63     
==========================================
+ Hits         6320     6376      +56     
- Misses       1749     1756       +7     

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