CI/TYP: pyright reportSelfClsParameterName
Fixes:

> pandas/core/arrays/_mixins.py:185:26 - warning: Instance methods should take a "self" parameter (reportSelfClsParameterName)

I'm not familiar with the function, could also be a `classmethod` @jbrockmendel 


should be a classmethod Ready and green.

Removes also an unused mypy ignore which caused an error on main.