Support the free-threaded Python build

[ngoldbaum]

It looks like blis does not currently ship cp313t wheels: https://pypi.org/project/blis/#files

Is that on your radar at all?

See https://py-free-threading.github.io for more information about supporting free-threaded Python in a library like Blis.

[crusaderky]

Next release will ship fully tested 3.14t wheels.
Nightly wheels are already available.

Leaving this issue open until the final release is published.