maybe "cls" arg shouldn't automatically be treated as non-annotatable

[anentropic]

here cls does not require annotation

@classmethod
def method(cls, whatever)
    ...

but here it does:

def regular_function(cls, whatever)
    ...

waterloo currently just has a dumb special case for cls and self args in first position, without considering context

...meaning if you annotate the cls arg of a regular function waterloo will complain it "has arg names which are inconsistent with the function signature"

(if you use other names than self and cls for method/classmethod first arg it probably breaks currently too)