Expose TreeMesh geometric intersections used for refine functions.

[jcapriot]

This PR unifies (and exposes) the geometric intersection tests used by the refine functionalities. The goal is to allow the user to see which cells actually intersected those geometric objects and use them to search for things.

This will expose operations to find cells that intersect with a

• Line (updated and fixes get_cells_along_line method not robust for tree mesh #346 )
• Box (updated)
• Ball
• Triangle
• Vertical Triangular Prism
• Tetrahedron
• Plane (which is a new addition to address MemoryError using mesh.plot_slice() with a TreeMesh of around 500,000 cells #355.)

It makes use of C++ templates and classes to reduce the repeated code for each of the different geometric objects.

[codecov]

Codecov Report

Attention: Patch coverage is 93.39623% with 7 lines in your changes are missing coverage. Please review.

Project coverage is 84.86%. Comparing base (300b64a) to head (9e3c19e).

Files	Patch %	Lines
discretize/mixins/mesh_io.py	88.00%	3 Missing ⚠️
discretize/tests.py	95.08%	3 Missing ⚠️
discretize/tree_mesh.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #356      +/-   ##
==========================================
- Coverage   85.12%   84.86%   -0.26%     
==========================================
  Files          36       36              
  Lines        8408     8472      +64     
==========================================
+ Hits         7157     7190      +33     
- Misses       1251     1282      +31     

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