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/src/lib.rs

@@ -2,7 +2,6 @@ mod digests;
 mod errors;
 #[cfg(feature = "fuse")]
 mod fuse;
-mod store_io;
 
 pub mod blobservice;
 pub mod directoryservice;
@@ -13,7 +12,6 @@ pub mod proto;
 
 pub use digests::B3Digest;
 pub use errors::Error;
-pub use store_io::TvixStoreIO;
 
 #[cfg(feature = "fuse")]
 pub use fuse::FUSE;