Define internal data format for photometry

[oliche]

We have settled on pynapple.

• [x] a TsdFrame or TsdSeries contains the signal.
• [x] if there is one or several reference channel(s) it is in a different Frame/Series
• [x] if there are several signal bands, the TsdFrame can be an array
• [x] the reference TsdFrame has the same dimensions as the signal frame
• [x] if only one of the signal bands has a meaningful reference, the empty reference is filled with NaNs
• [x] column names should be rois or regions names
• [ ] We need to look into the possibility of attaching a "trace header" metadata dictionary to the Pynapple object.
• [ ] Create an integration test passing the synthetic dataset through common pipeline

[grg2rsr]

metadata support for pynapple is coming soon (merged PR at their repo)