Support free threaded Python versions like '3.13t'

[colesbury]

Python wheels, pyenv, and a number of other tools use 't' in the Python version number to identify free threaded builds. For example, '3.13t', '3.14.0a1', '3.14t-dev'.

This PR supports that syntax in actions/setup-python, strips the "t", and adds "-freethreading" to the architecture to select the correct Python version.

See #771 and actions/python-versions#319

[renxida]

Meanwhile, if you can't wait, here at https://github.com/nod-ai/shark-ai/actions/workflows/ci_linux_x64_nogil-libshortfin.yml

we are using

    - name: Setup Python
      uses: deadsnakes/action@e640ac8743173a67cca4d7d77cd837e514bf98e8 # v3.2.0
      with:
        python-version: "3.13-dev"
        nogil : true

[rgommers]

If anyone needs the functionality in this PR, I'd recommend to use https://github.com/Quansight-Labs/setup-python. That is a fork of this action with the sole purpose of providing the functionality in this PR (free-threading support) until this PR gets merged (see this issue for context).

Data point for reviewers: we've exercised this PR quite heavily by now in projects like NumPy and SciPy, on Linux, macOS and Windows (x86-64 and aarch64/arm64), and it's been working smoothly to date.

[priyagupta108]

Hi @colesbury 👋,
Thank you for your valuable contribution!
During our testing, we observed that the changes in this PR do not support specifying the patch version (e.g., 3.13.1t) for the python-version input for the free-threaded binary. Please ensure that the python-version input values align with the existing input syntax.
Additionally, To keep the documentation up-to-date, please update this PR to incorporate the corresponding documentation updates.

Thank you!

[ddelange]

Also noting here that 3.13 and 3.13t currently don't live happily next to each other on Windows: Quansight-Labs#5 (comment)

[colesbury]

Hi @priyagupta108, thank you for reviewing the PR. I've fixed the handling of versions like 3.13.1t and added a test for that. I've also updated the README and "advanced-usage" documentation.