update UnitWaveformFeaturesGroup to be compatible with ClusterlessDecodingV1

[gshvarts]

Is your feature request related to a problem? Please describe.
I'm working on populating ClusterlessDecodingV1 with an encoding interval from a behavior session and a decoding interval from a sleep session. To do this, I'd like to combine the UnitWaveformFeatures from the two distinct interval lists (which have already been processed separately) using UnitWaveformFeaturesGroup. As it currently is, when I feed this wf group into ClusterlessDecodingV1, it thinks that all of the sort groups from one epoch are distinct from the other epoch. For example, I only have ~40 sort group ids in general for this day however when I do ClusterlessDecodingV1().fetch_spike_data, it returns ~80 spike time arrays.

Describe the solution you'd like
I'd like UnitWaveformFeaturesGroup to compare the sort group ids between the epochs that are being combined (maybe with some checks that you aren't just combining sort groups across different animals / dates, etc. that wouldn't make sense) and concatenate the spike times and waveform features across identically-named sort groups, as if they are coming from one larger combined epoch.

Describe alternatives you've considered
An alternative to this would be to process the run and sleep epochs as one larger interval and push it through the whole spike sorting pipeline, which I think would be possible but is redundant and time consuming if the data is already processed from running each epoch through the spike sorting pipeline separately.