refactor(tvix/{cli,store}): move TvixStoreIO to tvix-cli crate

This trait is eval-specific, there's no point in dealing with these
things in tvix-store.

This implements the EvalIO interface for a Tvix store.
The proper place for this glue code (for now) is tvix-cli, which knows
about both tvix-store and tvix-eval.

There's one annoyance with this move: The `tvix-store import` subcommand
previously also used the TvixStoreIO implementation (because it
conveniently did what we wanted).
Some of this code had to be duplicated, mostly logic to calculate the
NAR-based output path and create the PathInfo object.

Some, but potentially more of this can be extracted into helper
functions in a shared crate, and then be used from both TvixStoreIO in
tvix-cli as well as the tvix-store CLI entrypoint.

Change-Id: Ia7515e83c1b54f95baf810fbd8414c5521382d40
Reviewed-on: https://cl.tvl.fyi/c/depot/+/9212
Tested-by: BuildkiteCI
Reviewed-by: tazjin <tazjin@tvl.su>
Autosubmit: flokli <flokli@flokli.de>

tvix/store/Cargo.toml

@@ -15,7 +15,6 @@ prost = "0.11.2"
 rayon = "1.6.1"
 sha2 = "0.10.6"
 sled = { version = "0.34.7", features = ["compression"] }
-tvix-eval = { path = "../eval" }
 thiserror = "1.0.38"
 tokio-stream = "0.1.14"
 tokio = { version = "1.28.0", features = ["rt-multi-thread", "net"] }