Re-enable image and audio in the viewer
The current caching mechanism from #1026  is almost never used:
a. the parquet index is stored in memory per worker and there are too many of them
b. the image/audio files are always recreated

Because of that the viewer was too slow for image and audio datasets and we disabled it in #1144 

To fix this issue we could
- [x] 1. store the parquet index on disk using a worker
- [x] 2. use the local parquet index in /rows
- [ ] 3. (optional) avoid reloading images/audio files that are already on disk
Re-enable image and audio in the viewer: The current caching mechanism from #1026  is almost never used:
a. the parquet index is stored in memory per worker and there are too many of them
b. the image/audio files are always recreated

Because of that the viewer was too slow for image and audio datasets and we disabled it in #1144 

To fix this issue we could
- [x] 1. store the parquet index on disk using a worker
- [x] 2. use the local parquet index in /rows
- [ ] 3. (optional) avoid reloading images/audio files that are already on disk