Refactor syncback instance handling for improved readability

- Consolidated function calls in `syncback_instance_to_path_with_stats` across multiple files for better clarity and maintainability.
- Streamlined the formatting of function arguments to enhance code readability in `api.rs`, `file_names.rs`, and `project.rs`.
- Updated tests to reflect changes in function call structure while ensuring existing functionality remains intact.

src/snapshot_middleware/project.rs

@@ -690,7 +690,7 @@ pub fn syncback_project<'sync>(
                 if parent_middleware != Middleware::Project {
                     let taken_names = taken_names_per_dir
                         .entry(parent_path.clone())
-                        .or_insert_with(std::collections::HashSet::new);
+                        .or_default();
                     let (child_snap, _needs_meta, dedup_key) = snapshot.with_base_path(
                         &parent_path,
                         new_child.referent(),