feat(tvix/castore/blobsvc): add object storage implementation

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>

tvix/castore/Cargo.toml

@@ -11,8 +11,10 @@ bstr = "1.6.0"
 bytes = "1.4.0"
 data-encoding = "2.3.3"
 digest = "0.10.7"
+fastcdc = { version = "3.1.0", features = ["tokio"] }
 futures = "0.3.30"
 lazy_static = "1.4.0"
+object_store = { version = "0.9.1", features = ["aws", "azure", "gcp", "http"] }
 parking_lot = "0.12.1"
 pin-project-lite = "0.2.13"
 prost = "0.12.1"
@@ -26,6 +28,7 @@ tower = "0.4.13"
 tracing = "0.1.37"
 url = "2.4.0"
 walkdir = "2.4.0"
+zstd = "0.13.0"
 
 [dependencies.fuse-backend-rs]
 optional = true