Module gc

Old module which contained some implementation details of the #[pyproto] module.

Prefer using the same content from pyo3::pyclass, e.g. use pyo3::pyclass::PyTraverseError instead of use pyo3::class::gc::PyTraverseError.

For compatibility reasons this has not yet been removed, however will be done so once https://github.com/rust-lang/rust/issues/30827 is resolved.

Re-exports

• pub use crate::pyclass::PyTraverseError;
• pub use crate::pyclass::PyVisit;