run test and docs CI on 3.14

[molpopgen]

This PR adds doc and test CI for 3.14.
Adding 3.14 required bumping some dependencies.
Unfortunately, we now have to pin ipython<9 or fix markup in the manual here and in demes-spec. (This is ultimately part of the root of #592.) I am kicking that can down the road for now.

Ideally, we'd be testing 3.10 and 3.14 here instead of 3.12 and 3.14. I have confirmed locally that the docs build with 3.14 and the uv.lock in this PR.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.81%. Comparing base (1689034) to head (166c1fa).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #595   +/-   ##
=======================================
  Coverage   99.81%   99.81%           
=======================================
  Files           5        5           
  Lines        1600     1600           
=======================================
  Hits         1597     1597           
  Misses          3        3           

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[grahamgower]

This will trigger the docs to be deployed multiple times. If you really want to test building on multiple python versions, then the docs build job will need to be separate from the deploy job.

[molpopgen]

I disabled 3.12 here. Ideally we'd test on more versions but that is more important for the actual test suite. Realistically anyone contributing a PR will be working on 3.13 or later.