DOC: Enforce Numpy Docstring Validation | pandas.api.extensions.ExtensionArray
- xref https://github.com/pandas-dev/pandas/issues/58539

fixes:
```
pandas.api.extensions.ExtensionArray._pad_or_backfill 
pandas.api.extensions.ExtensionArray._reduce
pandas.api.extensions.ExtensionArray._values_for_factorize
pandas.api.extensions.ExtensionArray.astype
pandas.api.extensions.ExtensionArray.dropna
pandas.api.extensions.ExtensionArray.dtype
```


Thanks @ivonastojanovic 