clippy: fix all warnings across all binaries

- &PathBuf → &Path in memory-search.rs signatures
- Redundant field name in graph.rs struct init
- Add truncate(false) to lock file open
- Derive Default for Store instead of manual impl
- slice::from_ref instead of &[x.clone()]
- rsplit_once instead of split().last()
- str::repeat instead of iter::repeat().take().collect()
- is_none_or instead of map_or(true, ...)
- strip_prefix instead of manual slicing

Zero warnings on `cargo clippy`.

src/graph.rs

@@ -371,7 +371,7 @@ impl Graph {
             same_community,
             delta_cc_source: cc_after_source - cc_before_source,
             delta_cc_target: cc_after_target - cc_before_target,
-            delta_gini: delta_gini,
+            delta_gini,
             assessment,
         }
     }