Remove support for returning non-int's in __int__/__index__()

[skirpichev]

Feature or enhancement

Proposal:

Like #109311. Deprecation was in 3.10 (#15636), so this will match preferred practice per PEP 387.

N.B. there was a suggestion to revert this such deprecations back. I any case, I believe it's good to decide either way in 3.15.

Has this already been discussed elsewhere?

I have already discussed this feature proposal on Discourse

Links to previous discussion of this feature:

https://discuss.python.org/t/about-type-conversion-special-methods/94212