feat(core): add internal routine for 3D grid generation

[imrn99]

Description

Scope: core

Type of change: feat

Content description: TODO

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 54 lines in your changes missing coverage. Please review.

Project coverage is 76.52%. Comparing base (2b7e7fc) to head (0472e4c).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
honeycomb-core/src/cmap/builder/grid.rs	0.00%	54 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #256      +/-   ##
==========================================
- Coverage   77.98%   76.52%   -1.46%     
==========================================
  Files          47       49       +2     
  Lines        6676     6855     +179     
==========================================
+ Hits         5206     5246      +40     
- Misses       1470     1609     +139     

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[imrn99]

TODO:

• add vertex insertion
• add another drawing of the expected IDs?
• wire the routines to the builder
• tests