Add a Zarr tile source.

[manthey]

This mostly reads omezarr (ome-ngff).

If you have a zarr directory, you can convert it to a single file via code like:

import zarr

zarrsrc = zarr.open(<input directory>)
zarrstore = zarr.storage.SQLiteStore(<output path>)
zarrdest = zarr.open(store=zarrstore, mode='w')
zarr.copy_all(zarrsrc, zarrdest)

The input directory should have a .zgroup file in it. The output directory is a sqlite3 db file, so perhaps is suffix should be .db or .zarr. This also works with zipped zarr directories.