Surface::ToElement: add //friction/ode/mu

[scpeters]

🎉 New feature

Follow-up to #1036

Summary

The mjcf_to_sdformat converter in gz-mujoco constructs DOME objects programmatically and then uses Root::ToElement serialize to an XML file. Currently the Surface class adds elements for //contact/collide_bitmask in Surface::ToElement, and this pull request adds //friction/ode/mu as a minimal approach to supporting friction parameters.

Test it

Run UNIT_Collision_TEST

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

Merging #1049 (6f3cd14) into main (e91782b) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #1049   +/-   ##
=======================================
  Coverage   83.47%   83.47%           
=======================================
  Files         148      148           
  Lines       18393    18396    +3     
=======================================
+ Hits        15353    15356    +3     
  Misses       3040     3040           

Impacted Files	Coverage Δ
src/Surface.cc	87.96% <100.00%> (+0.27%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update e91782b...6f3cd14. Read the comment docs.