Drop Python 3.9, support Python 3.14 and 3.14t

[pquentin]

No description provided.

[A5rocks]

I don't see anything wrong here. (Though IMO you should check out uv's pip-compile replacement for the test-requirements.txt file, so that the locked dependencies don't vary based on the runtime Python version)

[cclauss]

I have been learning that it is quite useful to test with pytest-run-parallel to be confident about free-threaded compatibility. -- https://py-free-threading.github.io/testing

Something like:
% uvx --with=pytest-run-parallel pytest --iterations=8 --parallel-threads=auto