A slice of a sliced dataset gets the original dataset's filenames #572
Description
In [1]: from dkist import load_dataset; from dkist.data.sample import VISP_BKPLX
In [2]: ds = load_dataset(VISP_BKPLX)
In [3]: len(ds.files)
Out[3]: 1700
In [4]: stokesI = ds[0]
In [5]: len(stokesI.files)
Out[5]: 425
In [6]: scan = stokesI[:, :, 0]
In [7]: len(scan.files)
Out[7]: 1700