Checkout alternative meshers

[Huite]

Mapbox earcut might be nice to include: https://pypi.org/project/mapbox-earcut/

It won't generate great meshes, but it's a cheap way to convert polygons into triangles.

[Huite]

An interesting approach I've come across can be found in:

Fabrice Jaillet, Claudio Lobos. Fast Quadtree/Octree adaptive meshing and re-meshing with linear
mixed elements. Engineering with Computers, 2021, ff10.1007/s00366-021-01330-wff. ffhal-03161623f

https://hal.science/hal-03161623/document

They have a C++ implementation, but numba should be relatively well suited to this problem (use structured arrays to store the tree, index instead of pointer, just like numba_celltree).

From the MODFLOW 6 perspective, the suggested transition patterns provide reasonable orthogonality, such that XT3D might not be required for the transitions. Although it's worth benchmarking whether introducing whether introducing three triangle cells is better than XT3D by connection.