Assigning a callable as a member of an invokable does not work properly.

[Leopold Haller]

The function wrapping code is broken in cases where one assigns a callable as a member of a class, e.g.,

@enact.register
def foo():
  return "foo"
  
@enact.register
@dataclasses.dataclass
class MyResource(enact.Resource):
  fun: Callable
  
MyResource(foo).fun()  # Breaks