python: fully support 3.14

[austin3dickey]

In #9613 we added preview support for Python 3.14. This is because it's still in prerelease, so a handful of test dependencies haven't published wheels for it yet, and our CI isn't set up to build them from source, so we skipped tests for them on 3.14:

• fastapi
• geopandas
• haystack
• ibis
• lightning
• pyarrow
• torch
• snowflake

(I think many of these are waiting on pyarrow; see their issue at apache/arrow#47438).

Once these test dependencies are ready, we should enable the tests by dropping the python_version < '3.14' in various requirements.txt files and ensuring they're all run successfully.

Once the tests are passing, we can first-class Python 3.14 in the New Project Flow by reordering the list in extensions/positron-python/src/client/pythonEnvironments/creation/provider/uvUtils.ts, dropping the (preview) language in the same file, and dropping the (preview) language in src/vs/workbench/browser/positronNewFolderFlow/utilities/uvUtils.ts.

Also we can run the Python Tests CI job on ['3.9', '3.14'] instead of ['3.9', '3.13', '3.14'].

[isabelizimm]

We will probably need to bump our pydantic version, due to this error: python/cpython#130881