Small cleanups to the external TreeMesh code, no functionality changes

[jcapriot]

Just a few small code formatting changes, and noticed that python wrapped refine functions were called twice within the cython file. It's likely that the C++ compilers optimized this out before though.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.61%. Comparing base (f588f8b) to head (f7a8eb6).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #400   +/-   ##
=======================================
  Coverage   86.61%   86.61%           
=======================================
  Files          91       91           
  Lines       18710    18710           
  Branches     2111     2111           
=======================================
  Hits        16205    16205           
  Misses       1820     1820           
  Partials      685      685           

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