Add uint24 support for DatasetArray-based formats (excepting ND)

[fm3]

uint24 is webknossos’ way of handling rgb images (3×8 bytes). This is a special case and the only case where channels are supported (except splitting them into multiple layers with a channelIndex).

However, since this is still actively used (e.g. for prediction outputs in voxelytics), we need to support it also for zarr3. This PR adds this special case for readBytesXYZ in DatasetArray. Limitation: not for datasets with additionalCoordinates (ND), compare #7280.

Steps to test:

• Explore https://static.webknossos.org/data/zarr_v3/l4dense_motta_et_al_demo
• All 3 layers should be viewable (the prediction layer is the uint24 rgb one)
• (Note that I tested it locally)

Issues:

• fixes Support loading Uint24 Zarr3 datasets #7371

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• Updated changelog
• Considered common edge cases
• Needs datastore update after deployment