feat(ffi): add Python 3.14 context watcher API

[florentinl]

Python 3.14 added a context watcher API for observing contextvars.Context switches.

This exposes the raw declarations in pyo3-ffi.

Relevant links:

• C API docs
• CPython header

[bschoenmaeckers]

This file should be moved to the cpython folder. To mirror upstream.

[florentinl]

This makes sense to me. Should i do it in this PR ? Or move it in a prior PR and then add the watcher API ?

[bschoenmaeckers]

This makes sense to me. Should i do it in this PR ? Or move it in a prior PR and then add the watcher API ?

Yes please, you can do it here.

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[florentinl]

The RustPython bindings still need to stay outside of the cpython module which is marked with #[cfg(not(any(Py_LIMITED_API, RustPython)))]. So I kept the previous context.rs just for RustPython for this reason.

Is this the correct approach in these cases ?

[bschoenmaeckers]

The RustPython bindings still need to stay outside of the cpython module which is marked with #[cfg(not(any(Py_LIMITED_API, RustPython)))]. So I kept the previous context.rs just for RustPython for this reason.

Is this the correct approach in these cases ?

RustPython only supports abi3/abi3t so these functions are not exposed. So you can remove all RustPython cfg attributes.

[bschoenmaeckers]

Thanks! LGTM