Fix review findings: wishlist qualifying count, improve docs, and lint cleanup

- Count only configs meeting min_count as qualifying in the wishlist
  copy-coverage check (previously ALL guid_to_rid entries inflated the
  denominator, producing phantom wishlist entries), pre-computed once
  per guid instead of per record
- Update stale write_improve_csv doc to match single-best-target
  behavior including cross-copy exclusion
- Borrow owned configs for the trash CSV join instead of cloning the Vec
- Build owned_final_configs via filter_map + flat_map without the
  throwaway intermediate Vec
- Remove runtime assertions on literal constants (clippy
  assertions_on_constants) and replace a redundant closure with the
  function reference (clippy redundant_closure)
- Apply rustfmt across the crate and drop a duplicated test-section header

src/user_data.rs

@@ -79,9 +79,7 @@ pub fn load_my_cars_data(path: &str) -> Result<MyCarsData, AppError> {
                         let config = format!("{e}{w}{c}");
                         owned_configs.entry(guid.to_string()).or_default().push(config);
                     } else {
-                        eprintln!(
-                            "Warning: locked card {guid} has incomplete tune data — skipped"
-                        );
+                        eprintln!("Warning: locked card {guid} has incomplete tune data — skipped");
                     }
                 }
             }