Feat: improve rotated inset support

[aleaf]

• add support for generating grids with a specified rotation around features of interest
• add support for rotated LGR models (LGR parent and inset with same rotation)
• generalize logic of snapping inset grids to parent grids to ensure that the inset grid is symmetrical about nearfield features of interest when it is created from those (using a buffer; instead of by specifying offset and nrow, ncol)
• other clean-up refactoring and improvements to testing

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 95.08197% with 12 lines in your changes are missing coverage. Please review.

Project coverage is 89.31%. Comparing base (d2d459e) to head (80d649d).

Files	Patch %	Lines
mfsetup/grid.py	91.01%	8 Missing :warning:
mfsetup/discretization.py	92.30%	1 Missing :warning:
mfsetup/mf6model.py	83.33%	1 Missing :warning:
mfsetup/mfmodel.py	96.77%	1 Missing :warning:
mfsetup/tests/test_pfl_mfnwt_inset.py	66.66%	1 Missing :warning:

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #79 +/- ## =========================================== + Coverage 89.14% 89.31% +0.16% =========================================== Files 64 64 Lines 12396 12545 +149 =========================================== + Hits 11050 11204 +154 + Misses 1346 1341 -5 ```

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