Add RefinedGridInfo class (for potential Hovmoller/zonal mean support)

[stephenworsley]

Adds the RefinedGridInfo class. This class is designed to better handle grids with particularly large cells. These grids would typically have large innacuracies due to the difference between lines of latitudes and great circles, and in some cases, e.g. full latitude/longitude bounds, these could not even be represented in ESMF. This class solves these problems by having their ESMF representations be a "refinement" of the original grid by either increasing the longitude resolution by a desired factor, or else by increasing the latitude resolution sufficiently to be representable. This becomes especially usefull in the case of deriving Hovmoller plots.

[codecov]

Codecov Report

Merging #165 (214deda) into main (2013e7b) will decrease coverage by 0.10%.
The diff coverage is 98.43%.

❗ Current head 214deda differs from pull request most recent head ce97590. Consider uploading reports for the commit ce97590 to get more accurate results

@@            Coverage Diff             @@
##             main     #165      +/-   ##
==========================================
- Coverage   99.51%   99.40%   -0.11%     
==========================================
  Files          27       28       +1     
  Lines        2469     2705     +236     
==========================================
+ Hits         2457     2689     +232     
- Misses         12       16       +4     

Impacted Files	Coverage Δ
.../experimental/unstructured_regrid/test_MeshInfo.py	100.00% <ø> (ø)
esmf_regrid/_esmf_sdo.py	95.54% <92.98%> (-1.63%)	⬇️
esmf_regrid/esmf_regridder.py	95.38% <100.00%> (+0.30%)	⬆️
esmf_regrid/experimental/io.py	100.00% <100.00%> (ø)
esmf_regrid/experimental/unstructured_scheme.py	99.16% <100.00%> (+0.05%)	⬆️
...egrid/tests/unit/_esmf_sdo/test_RefinedGridInfo.py	100.00% <100.00%> (ø)
.../tests/unit/experimental/io/test_round_tripping.py	100.00% <100.00%> (ø)
...nstructured_scheme/test_GridToMeshESMFRegridder.py	100.00% <100.00%> (ø)
...nstructured_scheme/test_MeshToGridESMFRegridder.py	100.00% <100.00%> (ø)
...ntal/unstructured_scheme/test__cube_to_GridInfo.py	100.00% <100.00%> (ø)
... and 2 more

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[trexfeathers]

Lint failure: see SciTools/iris#4668

[trexfeathers]

Hi @stephenworsley, here's half a review (pre force-push).

[trexfeathers]

Apparently I was closer to finishing than I thought! Here's the final comment.

[trexfeathers]

Excellent work as usual @stephenworsley!