Zarr backend follow-up: tech

[fm3]

Follow-up for reading zarr-datasets in wk backend:

• cache clear for datavaults (when password for an account changes or the data vault breaks for some reason)
• double-check that fill value is used if chunk does not exist
• support string-encoded fill values
• perf: async cache, for file systems, handles – use akka-caching (caution: Futures all around, needs actorSystem)
• do not depend on jzarr, instead on its dependencies itself (only those we use) Do not depend on jzarr, use jblosc, ucarCdm directly #6152
• where to store file systems / file system provider ref
• perf optimization: skip allocating buffer if single-bucket request

[fm3]

I’d say with #6152 and #6165 the two most important parts of this issue are taken care of. Let’s schedule it again when we feel that the other checkboxes are relevant enough :)

[fm3]

I split the remaining parts of this issue into #6989 and #6990