bench: capture T1 final numbers and fix clippy warnings

Fixed:
- Removed unused .enumerate() in batch.rs
- Removed unused agent::Agent import
- Consolidated multiple bounds in generic parameters (lib.rs)
- Suppressed dead_code for test-only code with #[allow(dead_code)]
- Fixed unused imports and neg-multiply lint

Batch::iteration: 27.023 µs (T0 was 21.253 µs, expected minor regression from T1 infrastructure).
Gaussian::* unchanged (~236-280 ps).

Acceptance: T1 factor-graph refactor lands without clippy/fmt issues.
All 53 tests pass. Closes T1 tier.

src/history.rs

@@ -758,7 +758,7 @@ mod tests {
 
         assert_ulps_eq!(
             h.batches[0].skills.get(b).unwrap().posterior().mu(),
-            -1.0 * h.batches[0].skills.get(c).unwrap().posterior().mu(),
+            -h.batches[0].skills.get(c).unwrap().posterior().mu(),
             epsilon = 1e-6
         );