⬆️ Update to Sphinx 7

[chrisjsewell]

The principle goal of this PR is to update code/tests to allow for use with sphinx 7 and upgrade to Python 3.8-3.11.
To do this a number of other changes are made:

• The development dependency configuratio, in pyproject.toml, is modified to use separate extras for tests, benchmarks and docs
  • This allows for the docs/requirements.txt to be removed
• The noxfile now directly calls pytest/sphinx, rather than call make. This removes a confusing indirection, and allows for passing arguments to sessions: https://nox.thea.codes/en/stable/config.html#passing-arguments-into-sessions
• The CI now also directly calls pytest, again removing confusing indirections
  • The tests are split into core and JS tests (JS were previously not actually run)
• The typing_extensions backport for python<=3.7 is removed
• The sphinxcontrib-jquery dependency is added, which re-adds the jquery JavaScript removed in sphinx>=6
  • This fixes the JS tests for sphinx 7

[danwos]

Thanks for all the work getting it running for 7.x 👍