Support client-side coloring thresholding for `ImagePredictions`

[ap--]

This relates to viewers implemented to show pado image predictions. It's actually not so complicated.

• [ ] write pyramidal zarr with as many dimensions as you want
• [ ] store in tar and create kerchunk spec
• [ ] serve decompressed raw data to openseadragon in frontend.
• [ ] Implement frontend filtering via: https://github.com/openseadragon/openseadragon/issues/1417