Add Rust support for type hinting objects

[IvanIsCoding]

In short, I learned recently about Objects for Type Hinting in Qiskit/rustworkx#1345 and they are not available in pyo3-ffi. Those specific types have been part of the Stable ABI since 3.9.

Currently, I can still achieve my goals by importing types.GenericAlias via the Python interpreter but I still think typing objects deserve to be included.

I am willing to contribute the Rust bindings if they are welcome.

[davidhewitt]

Yep a PR to add these to pyo3-ffi seems straightforward. Going further, a way to define __class_getitem__ that's similar to python might be nice (e.g. by doing it with #[pyclass(generic)] as an option)

[ngoldbaum]

Yep a PR to add these to pyo3-ffi seems straightforward.

I recently had to touch pyo3-ffi a bunch to add support for free-threaded Python. Please feel free to ping me if you get stuck - although genericaliasobject.h looks pretty straightforward!