Expand dataframe-indexing type-lists

Changes look good.  Led to a question about possibly missing point indexing types to match the new slices (eg, if we have `slice(float)`, why not `np.array(float)`?)

_Originally posted by @bkmartinjr in https://github.com/single-cell-data/SOMA/pull/141#pullrequestreview-1314273242_
            