More tree refine functions

[jcapriot]

This adds more refinement functions for tree meshes.

• Line segment (determines whether a line segment and a cell intersect)
• triangle (determines whether a triangle and a cell intersect)
• Tetrahedron (determines whether a tetrahedron and a cell intersect)

They all are "exact" to floating point precision. Using the Separating Axis Theorem to determine the triangle and tetrahedron intersections.

The triangle and tetrahedron should make it natural to extend to any polyhedron body (Because those can always be broken into multiple triangles/tetrahedrons).

I think the next step is to update the refine_tree_xyz function and split it off into the three individual helper functions (at which point we would deprecate refine_tree_xyz).

[codecov]

Codecov Report

Merging #296 (98fb0d9) into main (febf017) will increase coverage by 0.62%.
The diff coverage is 96.98%.

@@            Coverage Diff             @@
##             main     #296      +/-   ##
==========================================
+ Coverage   84.41%   85.04%   +0.62%     
==========================================
  Files          36       36              
  Lines       11014    11090      +76     
==========================================
+ Hits         9297     9431     +134     
+ Misses       1717     1659      -58     

Impacted Files	Coverage Δ
discretize/View.py	0.00% <ø> (ø)
discretize/base/base_regular_mesh.py	84.69% <ø> (ø)
discretize/mixins/omf_mod.py	80.24% <ø> (ø)
discretize/utils/coordinate_utils.py	88.88% <ø> (ø)
discretize/tests.py	79.11% <66.66%> (ø)
discretize/mixins/mpl_mod.py	72.50% <86.66%> (ø)
discretize/mixins/vtk_mod.py	87.85% <93.02%> (ø)
discretize/cylindrical_mesh.py	94.14% <96.15%> (ø)
discretize/unstructured_mesh.py	99.11% <97.01%> (ø)
discretize/_extensions/tree_ext.pyx	84.22% <100.00%> (+2.35%)	⬆️
... and 12 more

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