feat(tvix/store): add NARCalculationService trait and impl

This adds a NARCalculationService trait, which will take a root node,
and provide a proto::CalculateNarResponse in return.

It also adds a NonCachingNARCalculationService implementation, that will
simply always render the NAR in memory to calculate the size and sha256,
without any caching.

Change-Id: Id1ffb18559212fa6001f70f2634bbc3dfd0aa343
Reviewed-on: https://cl.tvl.fyi/c/depot/+/8096
Reviewed-by: raitobezarius <tvl@lahfa.xyz>
Tested-by: BuildkiteCI

tvix/store/Cargo.toml

@@ -9,19 +9,21 @@ name = "tvix_store"
 [dependencies]
 anyhow = "1.0.68"
 blake3 = { version = "1.3.1", features = ["rayon", "std"] }
-data-encoding = "2.3.3"
-lazy_static = "1.4.0"
 clap = { version = "4.0", features = ["derive", "env"] }
+count-write = "0.1.0"
+data-encoding = "2.3.3"
+fastcdc = "2.0.0"
+lazy_static = "1.4.0"
 prost = "0.11.2"
+sha2 = "0.10.6"
 sled = { version = "0.34.7", features = ["compression"] }
 nix-compat = { path = "../nix-compat" }
 thiserror = "1.0.38"
 tokio-stream = "0.1.11"
 tokio = { version = "1.23.0", features = ["rt-multi-thread"] }
 tonic = "0.8.2"
-tracing-subscriber = "0.3.16"
 tracing = "0.1.37"
-fastcdc = "2.0.0"
+tracing-subscriber = "0.3.16"
 
 [dependencies.tonic-reflection]
 optional = true