feat(lib): TriangleMesh.{center,add_ground} methods and fixes

[jeertmans]

No description provided.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.48%. Comparing base (e36e821) to head (b69c2af).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #452      +/-   ##
==========================================
+ Coverage   86.41%   86.48%   +0.07%     
==========================================
  Files          32       32              
  Lines        3165     3189      +24     
==========================================
+ Hits         2735     2758      +23     
- Misses        430      431       +1     

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[codspeed-hq]

Merging this PR will not alter performance

✅ 15 untouched benchmarks

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_{Comparing add_ground (b69c2af) with main (e36e821)}