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/neuro.rs

@@ -275,7 +275,7 @@ fn format_health_section(store: &Store, graph: &Graph) -> String {
     for (i, &count) in buckets.iter().enumerate() {
         let lo = i as f32 / 10.0;
         let hi = (i + 1) as f32 / 10.0;
-        let bar: String = std::iter::repeat('█').take((count as usize) / 10).collect();
+        let bar = "█".repeat((count as usize) / 10);
         out.push_str(&format!("  {:.1}-{:.1}: {:4} {}\n", lo, hi, count, bar));
     }