MultiUSMesh fixes and test

[sseraj]

Purpose

MultiUSMesh was not used or tested, so it broke in several ways over the years. The main fixes here are related to imports, file I/O, and cgns_utils.

I also bumped the version number, and I will make a new release once this is merged.

Type of change

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (non-backwards-compatible fix or feature)
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no API changes)
• Documentation update
• Maintenance update
• Other (please describe)

Testing

I added a test using the Onera M6 mesh from the MACH-Aero overset tutorial. The test follows the same structure as the USMesh tests:

1. Regression testing the initial and warped coordinates
2. Complex-step verification of the AD

One of the mesh warping instances uses non-default aExp and bExp, which adds test coverage for the feature added in #64. I took this opportunity to test a bunch of other non-default options as well.

Checklist

• I have run flake8 and black to make sure the code adheres to PEP-8 and is consistently formatted
• I have run unit and regression tests which pass locally with my changes
• I have added new tests that prove my fix is effective or that my feature works
• I have added necessary documentation

[codecov]

Codecov Report

Merging #66 (3367f42) into master (71640df) will increase coverage by 27.71%.
The diff coverage is 93.33%.

@@             Coverage Diff             @@
##           master      #66       +/-   ##
===========================================
+ Coverage   45.72%   73.43%   +27.71%     
===========================================
  Files           6        6               
  Lines         748      753        +5     
===========================================
+ Hits          342      553      +211     
+ Misses        406      200      -206     

Impacted Files	Coverage Δ
idwarp/MultiUnstructuredMesh_C.py	91.66% <ø> (+41.66%)	⬆️
idwarp/UnstructuredMesh.py	62.73% <ø> (+1.65%)	⬆️
idwarp/MultiUnstructuredMesh.py	84.61% <92.85%> (+76.38%)	⬆️
idwarp/__init__.py	100.00% <100.00%> (ø)

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[lamkina]

This looks good to me.

[awccopp]

Everything here looks good

[marcomangano]

@awccopp @lamkina feel free to go ahead and merge