Support Python 3.13t (free-threaded mode)

[stephen29xie]

Should we support Python 3.13t?

from https://docs.python.org/3/whatsnew/3.13.html#free-threaded-cpython

CPython now has experimental support for running in a free-threaded mode, with the global interpreter lock (GIL) disabled. This is an experimental feature and therefore is not enabled by default. The free-threaded mode requires a different executable, usually called python3.13t or python3.13t.exe.

[MiWeiss]

It would already be nice if "standard" python 3.13 (without the experimental feature) was supported.