feat(tvix/store/pathinfoservice): implement NixHTTPPathInfoService

NixHTTPPathInfoService acts as a bridge in between the Nix HTTP Binary
cache protocol provided by Nix binary caches such as cache.nixos.org,
and the Tvix Store Model.
It implements the [PathInfoService] trait in an interesting way: Every
[PathInfoService::get] fetches the .narinfo and referred NAR file,
inserting components into a [BlobService] and [DirectoryService], then
returning a [PathInfo] struct with the root.
Due to this being quite a costly operation, clients are expected to
layer this service with store composition, so they're only ingested
once.
The client is expected to be (indirectly) using the same [BlobService]
and [DirectoryService], so able to fetch referred Directories and Blobs.
[PathInfoService::put] and [PathInfoService::nar] are not implemented
and return an error if called.

This behaves very similar to the nar-bridge-pathinfo code in nar-bridge,
except it's now in Rust.

Change-Id: Ia03d4fed9d0657965d100299af97cd917a03f2f0
Reviewed-on: https://cl.tvl.fyi/c/depot/+/10069
Tested-by: BuildkiteCI
Autosubmit: flokli <flokli@flokli.de>
Reviewed-by: raitobezarius <tvl@lahfa.xyz>

tvix/store/Cargo.toml

@@ -32,6 +32,8 @@ tvix-castore = { path = "../castore" }
 url = "2.4.0"
 walkdir = "2.4.0"
 async-recursion = "1.0.5"
+reqwest = { version = "0.11.22", features = ["rustls-tls", "stream"], default-features = false }
+xz2 = "0.1.7"
 
 [dependencies.fuse-backend-rs]
 optional = true