Add return_inverse to .unique in EA interface closes
- [x] closes #24245 
- [x] tests added / passed
- [x] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing.html#code-standards) for how to run them
- [ ] whatsnew entry

i am not sure how this PR helps here. this *already* raises an error if you try to use the parameter. In the original issue, it was stated that it 
> should be adapted to allow for the possibility of the return_inverse-kwarg.

I will try to work on the actual implementation if I can.  Looking at the implementation of `ExtensionArray.unique()`

> def unique(self: ExtensionArrayT) -> ExtensionArrayT:
        """
        Compute the ExtensionArray of unique values.
        Returns
        -------
        uniques : ExtensionArray
        """
        uniques = unique(self.astype(object))
        return self._from_sequence(uniques, dtype=self.dtype)

My suggestion would be to reverse `uniques` before it's passed to `self._from_sequence()`. Since `uniques` is a sequence of scalars, simply doing `uniques = uniques[::-1]` would reverse the values before being parsed into an ExtensionArray. Please let me know if that would work, and I will make changes accordingly. > In the original issue, it was stated that it
> 
> > should be adapted to allow for the possibility of the return_inverse-kwarg.
> 
> I will try to work on the actual implementation if I can.

I am not sure we want to support this api, we don't anywhere else.