Zarr streaming editable mapping support

[leowe]

URL of deployed dev instance (used for testing):

• https://___.webknossos.xyz

Steps to test:

• Go to a volume annotation with a mapping file in webknossos
• edit the segmentation and create a new segment
• request a bounding box that contains that segment, e.g. http://localhost:9000/tracings/volume/zarr/e1d6f00c-84ad-494c-9134-a9deefa4ecc7/1/0.2.4.1?token=secretSampleUserToken
• save response and check whether it contains the new segment, e.g. in python

import numpy as np

f = open("file.bin", "r")
a = np.fromfile(f, dtype=np.uint32)

Issues:

• fixes Mappings for Volume annotation zarr streaming #6225

---

• Needs datastore update after deployment
• Ready for review

[fm3]

This looks good to me already :) I added one qustion about empty fallback layer buckets, could you have a look?
I did not yet get to testing this, I hope I will get to that in the coming days.

[fm3]

Works for me 🎉 thanks for the easy-to-follow steps to test! :)
I added a few more small suggestions for the code

[fm3]

🎉