feat(nix-daemon): Implement QueryPathInfo and IsValidPath.

Change-Id: Ia601e2eae24a2bc13d8851b2e8ed9d6c1808bb35
Reviewed-on: https://cl.tvl.fyi/c/depot/+/12745
Reviewed-by: flokli <flokli@flokli.de>
Autosubmit: Vladimir Kryachko <v.kryachko@gmail.com>
Tested-by: BuildkiteCI

tvix/nix-compat/src/nix_daemon/mod.rs

@@ -1,8 +1,18 @@
+pub mod worker_protocol;
+
+use std::io::Result;
+
+use types::UnkeyedValidPathInfo;
+
+use crate::store_path::StorePath;
+
 pub mod handler;
 pub mod types;
-pub mod worker_protocol;
 
 /// Represents all possible operations over the nix-daemon protocol.
 pub trait NixDaemonIO {
-    // TODO add methods to it.
+    fn query_path_info(
+        &self,
+        path: &StorePath<String>,
+    ) -> impl std::future::Future<Output = Result<Option<UnkeyedValidPathInfo>>> + Send;
 }