* Add a missing setupmethod decorator
* Improve the decorator typing
This will allow type checkers to understand that the decorators return
the same function signature as passed as an argument. This follows the
guidelines from
https://mypy.readthedocs.io/en/stable/generics.html#declaring-decorators.
I've chosen to keep a TypeVar per module and usage as I think
encouraged by PEP 695, which I hope is accepted as the syntax is much
nicer.
