Index fallbacks with Intervals

[Tiri1992]

• closes Indexing on series where index is output from pd.cut  #27437 (Replace xxxx with the Github issue number)
• Tests added and passed if fixing a bug or adding a new feature
• All code checks passed.
• Added type annotations to new arguments/methods/functions.
• Added an entry in the latest doc/source/whatsnew/vX.X.X.rst file if fixing a bug or adding a new feature.

Summary

Looks to fix #27437 where the integer index should fallback to positional. I identified that the private method _should_fallback_to_positional returned the expression return self.dtype.subtype.kind in ["m", "M"] which was missing the numpy.dtype.kind for single integers and floats as expressed here.

However, extending the list with ["i", "f"] caused the character count to exceed 88, hence extracting this out in the previous line and storing as a variable to reference.

Tests are also included which aims to mimic the example given in the issue where the series is constructed with a CategoricalIndex with intervals.

Also, this is my first time contributing to the project so would appreciate feedback 👍

Edit

There are a couple things I need to fix

• Remove .loc[index] from unittest as this wasn't the desired property
• Investigate why other tests are failing