fix(cvfdutil): add non-convergence check to shapefile_to_cvfd

[wpbonelli]

Test the hanging node check on Voronoi grids. Mention that failure is possible with grids that have artifacts like near-duplicate vertices. Add an optional non-convergence check to the method. I figure it could be always on, as it only triggers if no progress is made by the algorithm, but not 100% sure about this, so kept it optional. Close #2427

[codecov]

Codecov Report

❌ Patch coverage is 44.44444% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 72.3%. Comparing base (556c088) to head (9a4865c).
⚠️ Report is 119 commits behind head on develop.

Files with missing lines	Patch %	Lines
flopy/utils/cvfdutil.py	44.4%	10 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2688      +/-   ##
===========================================
+ Coverage     55.5%    72.3%   +16.8%     
===========================================
  Files          644      667      +23     
  Lines       124135   130318    +6183     
===========================================
+ Hits         68947    94290   +25343     
+ Misses       55188    36028   -19160     

Files with missing lines	Coverage Δ
flopy/utils/cvfdutil.py	81.0% <44.4%> (-1.6%)	⬇️

... and 562 files with indirect coverage changes

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