Add support nogil mode in JAX for Python 3.13

[vfdev-5]

The idea is to add a support of nogil mode in JAX for Python 3.13. According to Jake and Peter, this would likely involve updates to both jaxlib and to nanobind.

• Add a CI job to run jax tests on python 3.13.0rc1 with free threading (or nogil). Similarly to scikit-learn, numpy or scipy (e.g. CI Add CPython 3.13 free-threaded build and remove historic nogil Python 3.9 build scikit-learn/scikit-learn#29191)

• Remaining FT bugs: https://github.com/jax-ml/jax/issues?q=is%3Aissue%20state%3Aopen%20label%3A%22free%20threading%22

Context:

• https://py-free-threading.github.io/
• https://docs.python.org/3.13/howto/free-threading-extensions.html

cc @jakevdp, @hawkinsp

---

• First stable jaxlib FT support version: 0.5.1 (cpython 3.13t), https://pypi.org/project/jaxlib/0.5.1/#files

[wjakob]

Nanobind's master branch now supports free-threading. Here is more information about the feature: https://nanobind.readthedocs.io/en/latest/free_threaded.html

[hawkinsp]

Thanks @wjakob . We're loving nanobind, by the way!