Update sphinx to 8.1

[davidorme]

Description

This PR:

• Updates pyproject.toml to use sphinx ^8.0.0, which is currently 8.1.3. We may need to be careful about the next release as it drop python 3.10 support. I think that is just that we'd have to run sphinx in python 3.11+ but something to keep in mind.

• Updates conf.py to:

  • Mute Sphinx 9 deprecation warnings
  • Remove some odd jupytext cruft that had crept in

• Adds the TODO extension to give nice clear TODO sections in docstrings. I've updated hydrology_model.py to use the directive and check it works and is rendering.

• Fixes a test bug - xarray is also upgraded in this and they have changed the wording on KeyErrors with Dataset objects.

The main reason for doing this was I upgraded to see if it fixed a bug. It didn't but we might as well upgrade it.

Fixes #727

Type of change

• 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

• Make sure you've run the pre-commit checks: $ pre-commit run -a
• All tests pass: $ poetry run pytest

Further checks

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

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.70%. Comparing base (39f2f88) to head (d49918b).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #729   +/-   ##
========================================
  Coverage    94.70%   94.70%           
========================================
  Files           73       73           
  Lines         4946     4946           
========================================
  Hits          4684     4684           
  Misses         262      262           

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[jacobcook1995]

LGTM!