Support Python 3.14

[leofang]

AFAIK CuPy is the only major user of fastrlock (correct me if I'm mistaken!), and it's again the time of the year for us to file a request 🙇

We are actively working on a vendored solution that could make it easier to support both new Python version as well as free threading (#19) at once, see cupy/cupy#8998. However, it seems it is easier to get PY314 support out of door if fastrlock can release a new wheel 😅

Thank you!

[seberg]

Just to note that CuPy is compiling to C++, so it now switched to C++ mutexes to avoid the dependency and unlock 3.14.
Which doesn't mean that 3.14 support isn't important for fastrlock, though :).