This uses the `object_store` crate to expose a tvix-castore BlobService
backed by object storage.
It's using FastCDC to chunk blobs into smaller chunks when writing to
it.
These are exposed at the .chunks() method.
Change-Id: I2858c403d4d6490cdca73ebef03c26290b2b3c8e
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11076
Reviewed-by: Connor Brewster <cbrewster@hey.com>
Tested-by: BuildkiteCI
Reviewed-by: Brian Olsen <me@griff.name>
