Add Physical Size Information to ZarrPixelSource

[ilan-gold]

User story
Right now, physical sizing is used internally as a convenience to the user. I am not sure this was such a hot idea in retrospect but in any case maybe we should add it for zarr. So we would add a meta tag to the ZarrPixelSource to allow for quick resolution internally of the rescaling.

Preferred solution
Duplicate what is done for TiffPixelSource regarding meta and physicalSizes for zarr and implement it for the latest OMENGFF spec(s).

Possible alternatives
We could just say this has to be done on a case-by-case basis for applications but we immediately run into our common issue - we are going to be the first people to do this twice i.e., would have to duplicate the effort between vitessce and avivator (if it is something we want in avivator)

@manzt would love a chime-in