Implement #[pyclass(generic)] for (complex) enums

[JPK314]

Support for runtime generic typing for structs was added last May in #4926. Is it planned to be added for (complex) enums as well? What are the complications that make this more of a challenge than structs?

[JPK314]

It was easy enough to add a simple implementation to my enum's pymethods that does the same thing the macro does for structs:

#[pyclass]
pub enum MyEnum {
    Var1 { x: u8 },
    Var2 {},
}

#[pymethods]
impl MyEnum {
    // python generics support
    #[classmethod]
    #[pyo3(signature = (key, /))]
    fn __class_getitem__<'py>(
        cls: &Bound<'py, PyType>,
        key: &Bound<'py, PyAny>,
    ) -> PyResult<Bound<'py, PyAny>> {
        Ok(PyGenericAlias::new(cls.py(), cls.as_any(), key)?.into_any())
    }
}

The method exists on all the variants because the variants inherit from the outer class, so this is sufficient.