Context

Python 3.13 includes provisional support for free-threading.
Once there is a version that supports free-threading in datetime, we should add it to our toolchain and update our C extensions for compatibility.

We can look to https://github.com/Quansight-Labs/free-threaded-compatibility for guidance.

https://github.com/python/cpython/issues/117398 tracks datetime support, and
https://github.com/Quansight-Labs/free-threaded-compatibility/issues/7 tracks most of our ecosystem dependencies.

This was inspired by Anthony Shaw's PyCon talk.

Definition of done

Add testing and Python 3.13 wheels with free-threading support.

Pitfalls

This is an emerging capability and there will be some rough edges and exploration.