gh-100268: Add is_integer method to int (#100439)

gh-100268: Add is_integer method to int (#100439)

This improves the lives of type annotation users of `float` - which type checkers implicitly treat as `int|float` because that is what most code actually wants. Before this change a `.is_integer()` method could not be assumed to exist on things annotated as `: float` due to the method not existing on both types.