TYP: Positional-only dunder binop method parameters

[jorenham]

This changes the __dunder__ binary operator methods of the types in __init__.pyi to all have positional-only parameters.

The reason this is important, is because type-checkers consider e.g.

class CanAdd(Protocol):
    def __add__(self, x: Any) -> Any: ...

to be incompatible with

class CanAlsoAdd(Protocol):
    def __add__(self, y: Any) -> Any: ...

because the parameters x and y are allowed to be used as keyword argument, i.e. their names matter.

[seberg]

LGTM, and the explanation sounds logical so putting it in, thanks.