Feature/pandas coords

[RobbieKiwi]

Closes #709

Changes proposed in this Pull Request

Fix the bug with pandas coords not being broadcast

Checklist

• Code changes are sufficiently documented; i.e. new functions contain docstrings and further explanations may be given in doc.
• Unit tests for new features were added (if applicable).
• A note for the release notes doc/release_notes.rst of the upcoming release is included.
• I consent to the release of this PR's code under the MIT license.

[FBumann]

@RobbieKiwi many ci fails. We might only fix this in #717

[FBumann]

@RobbieKiwi Thanks for the PR.

I would like to rewrite some of it to be more efficient:

def _sanitize_pandas(arr: pd.Series | pd.DataFrame) -> DataArray | None:
    names = list(arr.index.names)
    if isinstance(arr, pd.DataFrame):
        names += list(arr.columns.names)
    if any(n is None for n in names):
        return None

    if isinstance(arr, pd.DataFrame):
        arr = arr.stack(list(range(arr.columns.nlevels)), future_stack=True)

    return arr.to_xarray()

Also, we need to take care that the dim order stays deterministic (see #719).
Id like to merge #710 first, then adjust it here so pandas gets transposed properly

[FBumann]

@RobbieKiwi Due to the close coupling with #710 i decided thats its easiest to combine both into a single PR.
I've ported your tests and made some small changes to your code. If you want to I'd love to get your review on it.