opt out from requiring the GIL on free-threaded Python

[davidhewitt]

As per PyO3/pyo3#5558 (comment)

I also reverted the abi3 feature; that should not be needed, if the segfault returns I want to investigate.

[lmmx]

Thanks for following up on this it seems I didn't after that answer was given!

I still have the venv in question set up to test

• removing abi3 got rid of the "⚠️ Warning: CPython 3.14t at /home/louis/dev/comrak/.venv/bin/python does not yet support a bi3 so the build artifacts will be version-specific." warning at the start of the build
• tests all pass 🎉