refactor(tvix/nix-compat): reorganize wire and bytes

Move everything bytes-related into its own module, and re-export
both bytes and primitive in a flat space from wire/mod.rs.

Expose this if a `wire` feature flag is set. We only have `async` stuff
in here.

Change-Id: Ia4ce4791f13a5759901cc9d6ce6bd6bbcca587c7
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11389
Autosubmit: flokli <flokli@flokli.de>
Reviewed-by: raitobezarius <tvl@lahfa.xyz>
Tested-by: BuildkiteCI
Reviewed-by: Brian Olsen <me@griff.name>

tvix/nix-compat/src/lib.rs

@@ -6,4 +6,6 @@ pub mod nixbase32;
 pub mod nixhash;
 pub mod path_info;
 pub mod store_path;
+
+#[cfg(feature = "wire")]
 pub mod wire;