Minimal implementation of hexagonal mesh

[GuySten]

Description

This PR is a minimal implementation of hexagonal mesh.
I took PR #3279 and tried to simplify it as best I could.

Fixes # (issue)

Checklist

• I have performed a self-review of my own code
• I have run clang-format (version 18) on any C++ source files (if applicable)
• I have followed the style guidelines for Python source files (if applicable)
• I have made corresponding changes to the documentation (if applicable)
• I have added tests that prove my fix is effective or that my feature works (if applicable)

[GuySten]

@ebknudsen, I would like to hear your thoughts about this PR.
Currently, I did not include C API because I feel that this PR is large enough.

[ebknudsen]

@GuySten Sure - I'd be happy to go through it. It'll be a day or two before I get to it - just so you know.

[GuySten]

This PR is ready for review.