Cannot filter on a RunTS dataset

[kujaku11]

Cannot apply a sps_filter on a dataset. Need to loop over channels within the RunTS when a filter is applied.

[kkappler]

Maybe we could add a decorator that checks the dtype of the xarray. If it is a dataset, cast to data array, run the function, cast back to dataset and return it. I wrote the opposite decorator in aurora (casts dataarray to dataset on input and returns dataarray and put it here