TST: upgrade all dev jobs to CPython 3.14

[neutrinoceros]

Hopefully this should already be stable. If not, it'll help identify packages that could use a hand with forward compatibility issues.

[neutrinoceros]

the one error that may be related is from reproject, where the built package appears non-functional at runtime:

_ ERROR collecting .tox/py314-reproject-dev/lib/python3.14/site-packages/reproject/spherical_intersect/setup_package.py _
.tox/py314-reproject-dev/lib/python3.14/site-packages/reproject/spherical_intersect/setup_package.py:4: in <module>
    from setuptools import Extension
E   ModuleNotFoundError: No module named 'setuptools'

setuptools isn't present at runtime, though that shouldn't be a problem since setup_package.py shouldn't be there either
FYI @astrofrog

[neutrinoceros]

opening for review as is. I'll report + fix the build issue on reproject later.

[neutrinoceros]

It seems like there are two different problems, compounding into a runtime error:

• reproject.spherical_intersect.setup_package ends up in the installed package (it should be build-only)
• pytest insists on collecting test cases from this module (even though its name doesn't contain "test"). I assume this is because doctest_plus is enabled, which I think implies all modules are collected from, but I cannot reproduce this locally yet, so there's possibly a third piece in this puzzle that's specific to how this repo runs things.

[neutrinoceros]

(the first point is addressable on the project's side, however)

[neutrinoceros]

got it. reproject also needs --doctest-ignore-import-errors (which it addopts on its own pytest config) to survive this, which is why it only shows up when testing it as an installed package with doctest enabled.