Infer send type in generator function decorated with effect

[Sune Debel]

E.g

from pfun.maybe import with_effect, Maybe
from typing import Generator, Any, TypeVar

A = TypeVar('A')
Maybes = Generator[Maybe[Any], Any, A]
def g() -> Maybe[int]:
    ...

@with_effect
def f() -> Maybes[int]:
    a = yield g()
    reveal_type(a)  # should be int