Refactor area boundary sides retrieval with `_geographic_sides` and `_projection_sides` methods

[ghiggi]

• [ ] Closes #xxxx
• [ ] Tests added
• [x] Tests passed
• [x] Passes git diff origin/main **/*py | flake8 --diff
• [ ] Fully documented

This PR introduces the methods:

• _get_geographic_sides
• _get_projection_sides

These two methods allow to retrieve the boundary sides for whatever pyresample area, whether is geostationary or not. In a future PR, these two methods will also include the logic to retrieve the boundary of AreaDefinition with out-of-Earth coordinates.

This PR:

• does not impact get_area_slices method
• does not impact the AreaSlicer and SwathSlicer class yet
• does not fix GEO boundary definition issues
• does not fix boundary retrieval for out-of-earth disk areas

BUT :

• _get_geographic_sides is called within get_bbox_lonlats
• So from now on, get_bbox_lonlats returns non-Inf sides vertices for geostationary area !
• Since get_edge_lonlats and boundary() depends on get_bbox_lonlats, they now also returns non-Inf GEO vertices
• Note that the order of boundary vertices of get_bbox_lonlats has not yet be fixed to be correct.

_get_geographic_sides

• it's required in the coming PR to create the SphericalBoundary class
• get_bbox_lonlats is gonna be deprecated in upcoming PRs

_get_projection_sides

• is not yet used and tested in this PR
• it's required for the coming PR to create the SphericalBoundary and PlanarBoundary class
• it's required for the coming PR to deprecate usage of get_edge_bbox_in_projection_coordinates in SwathSlicer/AreaSlicer
• it's required for the coming PR to deprecate usage of get_geostationary_bounding_box_in_proj_coords in AreaSlicer

[codecov[bot]]

Codecov Report

Attention: 10 lines in your changes are missing coverage. Please review.

Comparison is base (c240c04) 94.09% compared to head (aee90a1) 94.06%.

Files	Patch %	Lines
pyresample/geometry.py	81.39%	8 Missing :warning:
pyresample/gradient/__init__.py	81.81%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #566 +/- ## ========================================== - Coverage 94.09% 94.06% -0.04% ========================================== Files 85 85 Lines 13235 13250 +15 ========================================== + Hits 12453 12463 +10 - Misses 782 787 +5 ``` | [Flag](https://app.codecov.io/gh/pytroll/pyresample/pull/566/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pytroll) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/pytroll/pyresample/pull/566/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pytroll) | `94.06% <84.12%> (-0.04%)` | :arrow_down: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pytroll#carryforward-flags-in-the-pull-request-comment) to find out more.

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[coveralls]

coverage: 93.644% (-0.03%) from 93.675% when pulling aee90a1879e3510a09e1a9ccdba2931342c28b33 on ghiggi:refactor-geometry-sides-creation into c240c0492ac5fd35add30d3c9fbcf3c45aba36ba on pytroll:main.

[ghiggi]

@djhoese ok now it works. Ready for review and eventually merge ;)

[djhoese]

Ugh, that's what I get for trying to fix something in the github GUI. Working on it...

[djhoese]

I'll merge this when CI passes. Another idea (for a much later PR) I had and maybe mentioned during out last meeting:

How useful are some of these helper methods outside of boundary creation? What if the new Boundary classes had a .from_area or .from_geometry classmethod or how we talked about a factory function (something like boundary_for_geometry(...))? All these little helper methods could be moved there and out of the geometry.py module.