Updates for python free threading

[jcapriot]

The only place free threading should throw us an issue is on modifying the structure of the TreeMesh, as multiple concurrent calls to a refine function will modify a c++ map which is not a thread safe operation. This PR adds a cython mutex lock to the locations that modify the structure of the mesh, and then marks our .pyx extension modules as safe for free threading.

[codecov]

Codecov Report

❌ Patch coverage is 98.66667% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 86.81%. Comparing base (267d976) to head (dff9c40).
⚠️ Report is 16 commits behind head on main.

Files with missing lines	Patch %	Lines
tests/cyl/test_cyl_io.py	94.44%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #403      +/-   ##
==========================================
+ Coverage   86.65%   86.81%   +0.16%     
==========================================
  Files          91       91              
  Lines       18769    18802      +33     
  Branches     2119     2119              
==========================================
+ Hits        16264    16323      +59     
+ Misses       1820     1801      -19     
+ Partials      685      678       -7     

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