Add stage_paths field to PatchSet struct in tests

- Introduced a new field, `stage_paths`, to the `PatchSet` struct in `patch_compute.rs` to track filesystem paths for staging.
- Updated test cases to initialize `stage_paths` alongside other fields, ensuring consistency in patch set creation.

These changes enhance the testing framework by providing additional context for staged paths in patch sets.

src/snapshot/patch_compute.rs

@@ -348,6 +348,7 @@ mod test {
             added_instances: Vec::new(),
             removed_instances: Vec::new(),
             stage_ids: std::collections::HashSet::new(),
+            stage_paths: Vec::new(),
         };
 
         assert_eq!(patch_set, expected_patch_set);
@@ -399,6 +400,7 @@ mod test {
             updated_instances: Vec::new(),
             removed_instances: Vec::new(),
             stage_ids: std::collections::HashSet::new(),
+            stage_paths: Vec::new(),
         };
 
         assert_eq!(patch_set, expected_patch_set);