feat(dis_properties): add grid method to get discretization properties

[jlarsen-usgs]

• returns dictionary of keyword arguments to build DIS, DISV, and DISU depending on grid type
• added cell .area calculation via shoelace algorithm to Grid
• remove deprecated flopy.mf6.utils/reference.py which housed "pre-modelgrid" spatial reference support for MF6 models

Mirrors support outlined in removed PR #2700

[codecov]

Codecov Report

❌ Patch coverage is 94.00000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 73.3%. Comparing base (556c088) to head (32a5609).
⚠️ Report is 197 commits behind head on develop.

Files with missing lines	Patch %	Lines
flopy/discretization/unstructuredgrid.py	90.4%	2 Missing ⚠️
flopy/discretization/vertexgrid.py	83.3%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2795      +/-   ##
===========================================
+ Coverage     55.5%    73.3%   +17.7%     
===========================================
  Files          644      659      +15     
  Lines       124135   132157    +8022     
===========================================
+ Hits         68947    96913   +27966     
+ Misses       55188    35244   -19944     

Files with missing lines	Coverage Δ
flopy/discretization/grid.py	75.4% <100.0%> (-0.6%)	⬇️
flopy/discretization/structuredgrid.py	54.5% <100.0%> (+7.1%)	⬆️
flopy/utils/voronoi.py	81.6% <100.0%> (+12.2%)	⬆️
flopy/discretization/vertexgrid.py	80.1% <83.3%> (-3.6%)	⬇️
flopy/discretization/unstructuredgrid.py	83.1% <90.4%> (+1.6%)	⬆️

... and 580 files with indirect coverage changes

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[jlarsen-usgs]

PR will close
#2388
#2661

[jdhughes-dev]

The grid methods and the cell area calculation look good. I checked area against areas I could work out by hand and it is right for a structured grid with variable row and column spacing and for a vertex grid holding a square and a triangle.

Removing flopy/mf6/utils/reference.py is overdue. It was deprecated in 3.9 for removal in 3.10+, we are at 3.11, and nothing in flopy imports it.

Two things before this goes in:

• .docs/code.rst still lists ./source/flopy.mf6.utils.reference.rst. The files under source/ are written by sphinx-apidoc at build time, so once the module is gone that line points at a document that is never generated. Read the Docs is not set to fail on warnings and the docs are not built on a pull request, so this will not turn up until after the merge.
• Patch coverage is 55%, mostly the new get_dis*_kwargs paths.

Should this go in the release that accompanies MODFLOW 6 6.8.0, or wait for the one after?

[jlarsen-usgs]

@jdhughes-dev

I'll work on some additional testing and clean up the docs for the removed reference.py module.

There isn't a big rush to get this one in, so feel free to move forward with the release if this PR isn't completed in time.