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 python-bidi could provide prebuilt wheels and confirm compatibility with python3.14t (the free-threaded ABI).

[MeirKriheli]

I would appreciate some help with that, not sure how it goes with pyo3.