grid_wrap: roundtrip tests

[mathause]

Note that the wrap functions do not strictly round trip data that is outside the -180..180/ 0..360 range.

• Closes #xxx
• Tests added
• Passes isort . && black . && flake8
• Fully documented, including CHANGELOG.rst

[codecov]

Codecov Report

Patch coverage: 75.00% and project coverage change: +0.16% 🎉

Comparison is base (0232bd5) 86.31% compared to head (46007a9) 86.48%.
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #273      +/-   ##
==========================================
+ Coverage   86.31%   86.48%   +0.16%     
==========================================
  Files          39       39              
  Lines        1549     1546       -3     
==========================================
  Hits         1337     1337              
+ Misses        212      209       -3     

Flag	Coverage Δ
unittests	86.48% <75.00%> (+0.16%)	⬆️

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Files Changed	Coverage Δ
mesmer/io/_load_cmipng.py	80.64% <75.00%> (+1.90%)	⬆️

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[mathause]

I think the failed rtd build is spurious - merging.