Support for patching over multiple datasets in Zarrs

[Mohinta2892]

Hello Dani!

Please can you extend the support for loading and patching from multiple datasets (such as labels and raw) stored within one zarr.

The zarr organisation may look like:

 filename.zarr
       - volumes
              - raw
              - labels
                   - neuron_ids

The datasets may also have associated attributes, such as offsets (for labels) and image resolution ( for raw).

An example can be found here

Best, Samia