feat(tvix/store/protos): add Deriver field to PathInfo

This uses the newly introduced StorePath message type to add a Deriver
field to the PathInfo message.

Support for validation is added to both the golang and rust
implementation. This includes extending unit tests.

Change-Id: Ifc3eb3263fa25b9eec260db354cd74234c40af7e
Reviewed-on: https://cl.tvl.fyi/c/depot/+/9647
Reviewed-by: Connor Brewster <cbrewster@hey.com>
Tested-by: BuildkiteCI

tvix/store/src/bin/tvix-store.rs

@@ -296,6 +296,7 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
                                 signatures: vec![],
                                 reference_names: vec![],
                             }),
+                            deriver: None,
                         };
 
                         // put into [PathInfoService], and return the PathInfo that we get back