refactor(tvix/castore/tests): let gen_*_service return Boxes

Only convert to and reuse an Arc<…> where needed.

Change-Id: I2c1bc69cca5a4a3ebd3bdb33d6e28e1f5fb86cb9
Reviewed-on: https://cl.tvl.fyi/c/depot/+/10514
Tested-by: BuildkiteCI
Autosubmit: flokli <flokli@flokli.de>
Reviewed-by: raitobezarius <tvl@lahfa.xyz>

tvix/store/src/proto/tests/grpc_pathinfoservice.rs

@@ -22,8 +22,8 @@ fn gen_grpc_service(
     let blob_service = gen_blob_service();
     let directory_service = gen_directory_service();
     Arc::new(GRPCPathInfoServiceWrapper::new(gen_pathinfo_service(
-        blob_service,
-        directory_service,
+        blob_service.into(),
+        directory_service.into(),
     )))
 }