Remove ome-zarr-py dependency

[will-moore]

As part of investigation into possible deprecation of ome-zarr-py, I wanted to see what it would take to remove the dependency from this repo.

In this PR, I have used 2 different approaches for the writing of images and label-images

• for OME-Zarr images, I've copied over the required code from ome-zarr-py. This is because we were already doing the writing of Zarr to disk and we just needed ome-zarr-py for adding metadata and generating a pyramid. Most of the write_* methods (write_multiscales_metadata, write_well_metadata, write_plate_metadata) were doing validation which isn't strictly needed in our usage. Also we could replace the validation by using ome-zarr-models-py in in future.
  The only other method we needed for creating image pyramids was resize() for resizing dask arrays.
  This is a relatively small amount of code, copied into this repo for now, but it could make sense to keep it or move it elsewhere if we decide to deprecate ome-zarr-py.

• for OME-Zarr label-images, I have used ngff-zarr to create the down-sampled pyramids from numpy data, and to write this to disk with multiscales metadata, replacing ome-zarr. write_multiscale_labels(). We now need to manually create the labels group etc and add image-label metadata since ngff-zarr has no support for reading/writing OME-Zarr labels.

ngff-zarr says Scaling is constrained by size of chunks - we do not scale below the chunk size but in practice, ngff-zarr simply uses smaller chunks for smaller resolutions.