refactor(tvix): introduce nix-compat crate

Move nixbase32 and store_path into this.

This allows //tvix/cli to not pull in //tvix/store for now.

Change-Id: Id3a32867205d95794bc0d33b21d4cb3d9bafd02a
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7964
Tested-by: BuildkiteCI
Reviewed-by: tazjin <tazjin@tvl.su>

tvix/store/src/lib.rs

@@ -1,6 +1,4 @@
-pub mod nixbase32;
 pub mod proto;
-pub mod store_path;
 
 pub mod dummy_blob_service;
 pub mod sled_directory_service;