Typeinterval part2
Is on top of https://github.com/pandas-dev/pandas/pull/46080

I believe the typing for `Interval` here is correct as it passes the tests created here:
https://github.com/microsoft/python-type-stubs/pull/167/

Leaving this as draft status as it requires #46080 to be approved.

Or a decision to go with #44922, in which case we kill #46080 and this one.


Looks pretty good @Dr-Irv! I'll look at part 1 tomorrow. > Looks pretty good @Dr-Irv! I'll look at part 1 tomorrow.

Thanks! other PR merged so pls rebase > other PR merged so pls rebase

all set and all green thanks @Dr-Irv keep em coming!