Merging this PR will not alter performance

✅ 125 untouched benchmarks

_{Comparing Person-93:no_std_ffi (ee47c67) with main (e742ed2)}

The ffi crate currently uses std::thread::park to work around the interpreter calling pthread_exit for python versions older than 3.14.

I can think of two ways to handle this.

• move the usage into the main crate
• use a feature-flag to conditionally use a separate crate that can sleep in no_std

The first way is technically a breaking change if anyone is using the PyGILState_Ensure method from the ffi crate as they would have to deal with pinned stack objects some other way, but I think it's simpler, so I will go with that one unless you object.

Neat, I'm glad this is mostly mechanical. I'll try to give this a once-over.

I agree with all of David's comments. I also think we need a CI job that compiles the crate with no_std. Might be worth adding that to the nox configuration so all the CI jobs do it if it's a pretty quick build.

The ffi crate will always compile with no_std if python >= 3.14 or wasm build. It's not feature-gated.