Add CPython 3.14

[mayeut]

It's time to add CPython 3.14 to manylinux images.

The issue will be closed once CPython 3.14.0 final is released.

The free-threaded (no GIL) build is also available.

EDIT: python 3.14.0b2 is currently available in the manylinux images

[andife]

@mayeut will cpython 3.14 dev also be available in manylinux2014 ?

[mayeut]

it's already in on all supported images (which include manylinux2014 images).