Start building for python 3.15 pre-release

[asmacdo]

3.15 release is scheduled for October 2026

My project has a dependency on rpds, and I'd like to start testing the upcoming release as early as possible, but first we need wheels for 3.15.

I gave it a shot, but fails, because pyo3 doesnt support 3.15 yet

[edgarrmondragon]

but first we need wheels for 3.15.

FWIW published wheels are not strictly needed. You can set PYO3_USE_ABI3_FORWARD_COMPATIBILITY=1 in the environment where you install your project's dependencies for testing.