Series.unique() with dtype “timedelta64[ns]” or “datetime64[ns]”

Part of migration to pandas 2.0

[Series.unique()](https://pandas.pydata.org/docs/reference/api/pandas.Series.unique.html#pandas.Series.unique) with dtype “timedelta64[ns]” or “datetime64[ns]” now returns TimedeltaArray or DatetimeArray instead of numpy.ndarray

cf #624 