`hydrotools.metrics` flags a `Pandas4Warning`

[jarq6c]

The hydrotools.metrics test suite is flagging this warning:

hydrotools/python/metrics/src/hydrotools/metrics/_validation.py:131: Pandas4Warning: Constructing a Categorical with a dtype and values containing non-null entries not in that dtype's categories is deprecated and will raise in a future version.
    s = pd.Series(

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html

The type transformation logic for categorical metrics may need to be revamped. It's likely inefficient, anyway.