remove 1.5 tests and types

[Dr-Irv]

Tested with pandas 2.0. Removed references to pandas 1.5, and removed types (NumericIndex related), creating special types for typing so we can track Index with int and Index with float

Updated the version number, but don't intend to do a release until we handle issues in #624

[twoertwein]

Personally, I wouldn't mind removing the typing-only classes (less perceive typing but more maintanable).

[twoertwein]

Thanks @Dr-Irv !

[Dr-Irv]

Personally, I wouldn't mind removing the typing-only classes (less perceive typing but more maintanable).

I started doing that. But we have methods that in 1.5 were dependent on Int64Index and Float64Index. If I switch to Index, then it creates all sorts of overload problems.

This is one of these cases where removing NumericIndex and its subclasses was not good from a typing perspective.

The _IntIndexType and _FloatIndexType classes are a step towards a generic index implementation, similar to how we have TimeStampSeries, TimeDeltaSeries, etc.