fix: region border plot

[pabloitu]

fixes #197. Now uses shapely to merge all cell polygons into one, and extract the borders. Floating point issues with coincident cell edges are sorted out by rounding up to 2 decimals.

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Fixes issue #197 #200.

Type of change:

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• New and existing unit tests pass locally with my changes

[wsavran]

docs are failing the build with this new function. i also think we need to add shapely to the requirements and the build. it's implicitly provided through cartopy but i think we want to explicitly put it with our distribution.

[pabloitu]

actually good that it failed the docs. For some reason it's failing in CA, which i didnt tested. Need to take a look further. Will put shapely in the reqs also.

[pabloitu]

build fail was because of plot_gridded_forecast tutorial, which loaded helmstetter from ascii. In this func, parsing the file made self-intersecting cell polygons. Fixed #200 and now boundaries can be plotted for NZ, Italy and california without problems.

[codecov-commenter]

Codecov Report

Base: 55.73% // Head: 55.73% // Decreases project coverage by -0.00% ⚠️

Coverage data is based on head (392850b) compared to base (74106b9).
Patch coverage: 64.70% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #199      +/-   ##
==========================================
- Coverage   55.73%   55.73%   -0.01%     
==========================================
  Files          20       20              
  Lines        3572     3594      +22     
  Branches      569      580      +11     
==========================================
+ Hits         1991     2003      +12     
- Misses       1460     1466       +6     
- Partials      121      125       +4     

Impacted Files	Coverage Δ
csep/core/regions.py	47.04% <54.54%> (+0.29%)	⬆️
csep/core/forecasts.py	57.38% <83.33%> (ø)

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[wsavran]

reviewed the pull request, everything looks good except for 2 pieces. first we need to add shapely to setup.py and the requirements.yml and i'll merge it.

[pabloitu]

done