Improve boundary conformity

[krober10nd]

• On termination, it's possible to repeatedly project only the boundary vertices back onto the 0-level set for better boundary conformity.

• See here what I did in Python.

https://github.com/krober10nd/SeismicMesh/blob/fa4cbc97a987d3468e6362fce6c76efe05f47bdf/SeismicMesh/generation/mesh_generator.py#L436

• It removes some of the "dents" that happen when meshing with an implicit domain.

Here's the function call:
https://github.com/krober10nd/SeismicMesh/blob/fa4cbc97a987d3468e6362fce6c76efe05f47bdf/SeismicMesh/generation/mesh_generator.py#L629

[krober10nd]

This is superseded by #264 which solves a 1D mesh generation problem prior to 2D meshing to gather pfix and egfix that conform in spacing with the mesh sizing function.