Add Python 3.14 free-threading build support

[ericbuehl]

With the release of Python 3.14, the new free-threaded (no-GIL) mode is becoming more widely used.

It would be great if this project could provide prebuilt wheels and confirm compatibility with python3.14t (the free-threaded ABI).

[daniel-sanche]

I'm not too familiar with the differences in free-threaded mode. Do you have a code snippet we can use to test that the build is working as expected?

[ericbuehl]

I'm not too familiar with the differences in free-threaded mode. Do you have a code snippet we can use to test that the build is working as expected?

This is a pretty comprehensive guide: https://py-free-threading.github.io

[daniel-sanche]

Ok, my impression is that this would involve more changes than just enabling the build, since we need to ensure our code isn't holding on to the GIL. So this likely isn't something that we will focus on in the near term