support reading zstd-compressed zarr2 datasets

[fm3]

I didn’t find details about the zarr2 specification for the zstd compressor, so I’m just taking what I saw in the example dataset (just "level"). That means that for datasets with non-integer level or a different feature like checksums it may still not work. Let’s work on that when we notice problems.

URL of deployed dev instance (used for testing):

• https://zarrzstd.webknossos.xyz

Steps to test:

• Add a zstd-compressed remote dataset, e.g. s3://janelia-cosem-datasets/jrc_mus-nacc-4/jrc_mus-nacc-4.zarr/
• Should load correctly (note: the contrast of that dataset is very low compared to the int16 data range)

Issues:

• fixes Support ZStandard Compression for Zarr (version 2) #7894

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• Updated changelog
• Needs datastore update after deployment

[MichaelBuessemeyer]

Aesome, works 🎉