Allow for cylindrical and spherical shell domains

[brosaplanella]

Description

Now we only throw and error for non zero-Neumann bcs if the boundary is at r = 0, which means cylindrical and spherical shells can be solved with any boundary condition. Also added some integration tests to check it works.

Fixes #3115

Type of change

Please add a line in the relevant section of CHANGELOG.md to document the change (include PR #) - note reverse order of PR #s. If necessary, also add to the list of breaking changes.

• New feature (non-breaking change which adds functionality)
• Optimization (back-end change that speeds up the code)
• Bug fix (non-breaking change which fixes an issue)

Key checklist:

• No style issues: $ pre-commit run (or $ nox -s pre-commit) (see CONTRIBUTING.md for how to set this up to run automatically when committing locally, in just two lines of code)
• All tests pass: $ python run-tests.py --all (or $ nox -s tests)
• The documentation builds: $ python run-tests.py --doctest (or $ nox -s doctests)

You can run integration tests, unit tests, and doctests together at once, using $ python run-tests.py --quick (or $ nox -s quick).

Further checks:

• Code is commented, particularly in hard-to-understand areas
• Tests added that prove fix is effective or that feature works

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (b6d4f3f) 99.71% compared to head (67dcb1c) 99.71%.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #3237   +/-   ##
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  Coverage    99.71%   99.71%           
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  Files          248      248           
  Lines        18861    18861           
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  Hits         18807    18807           
  Misses          54       54           

Files Changed	Coverage Δ
pybamm/discretisations/discretisation.py	99.78% <100.00%> (ø)

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[brosaplanella]

This is now ready to review

[valentinsulzer]

It's a bit strange to have a solver inside this test. Not the end of the world but would be better without, so that this is really a unit test (and not dependent on the solver). Is there another way to test the same thing?

[brosaplanella]

It's an integration test though, isn't it fine to have a solver there?

[valentinsulzer]

Ah yes true, then it's fine