chore(tvix/store): migrate import.rs and tests/pathinfo.rs to rstest

Also, rename the DUMMY_NAME constant in the fixtures to DUMMY_PATH,
which aligns more with the ToString representation and from_bytes
conversions we have on StorePath[Ref].

Change-Id: I39763c9dfa84c5d86f2fd0171b3a4d36fd72f267
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11464
Autosubmit: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI
Reviewed-by: Connor Brewster <cbrewster@hey.com>

tvix/store/src/pathinfoservice/grpc.rs

@@ -207,7 +207,7 @@ mod tests {
         };
 
         let path_info = grpc_client
-            .get(fixtures::DUMMY_OUTPUT_HASH)
+            .get(fixtures::DUMMY_PATH_DIGEST)
             .await
             .expect("must not be error");