Override __int__ and __index__ for bool in builtins.pyi

[jonathandung]

Such that the fact that they only return 1 for True and 0 for False may be represented without violating the Liskov Substitution Principle. This change is motivated by astral-sh/ty#4048, from which I learnt no type checker supports the inference of the value of booleans in integer operation context, but that may be fixable by a stub-side modification.

[jonathandung]

I do not understand the mypy failure involving the term "erased type".

[github-actions]

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉

[srittau]

This is a mypy bug, see python/mypy#14764. You may try to ignore this error using # type: ignore[misc] with a link to the bug.

[AlexWaygood]

To be clear, I don't think this, on its own, would help ty much with regards to the linked issue. I don't believe we currently look at these dunders when implementing our special casing for arithmetic regarding literal integers or bools. I'm also not sure we'd want to start looking at these dunders if we were to implement the feature request in the linked issue: I think there are probably simpler ways of achieving that goal.

This PR might be worth doing anyway, though; I don't have a position on that