Whenever this encounters an open_read(), it'll first check for more
granular chunking. If there's more granular chunking data available, a
ChunkedReader is constructed (which supports seeking backwards).
This currently is still a bit stupid, and doesn't compose, as
`ChunkedReader` uses `self` as the `BlobService` to ask for the
individual chunks.
In store composition future, we might want to compose this differently,
essentially constructing `ChunkedReader` with another `BlobService`
representing the entire hierarchy, so there's a chance to locally cache
things, and do less requests.
Change-Id: I22e0df4d6245f666d083b4f0b7114d3ac41d1dce
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11185
Tested-by: BuildkiteCI
Reviewed-by: Connor Brewster <cbrewster@hey.com>
82f8ce8b7d