Add FVO2 for curved 3D meshes

[ArturYeritsyan]

I have added fvO2 solver for the 3D StructuredMesh, P4estMesh, T8codeMesh and an example on a real curved mesh.
And a convergence test done on a curved mesh:

[github-actions]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.03%. Comparing base (9e4eec3) to head (132c1a2).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2755   +/-   ##
=======================================
  Coverage   97.03%   97.03%           
=======================================
  Files         568      569    +1     
  Lines       44429    44471   +42     
=======================================
+ Hits        43109    43151   +42     
  Misses       1320     1320           

Flag	Coverage Δ
unittests	97.03% <100.00%> (+<0.01%)	⬆️

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[DanielDoehring]

The tests are also missing right now

[ArturYeritsyan]

i have added the convergence test.

[DanielDoehring]

i have added the convergence test.

Can you also add a test for the free stream elixir? This way we make sure this property is also preserved in the future.

[ArturYeritsyan]

yes i have added it

[DanielDoehring]

Thanks @ArturYeritsyan !