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/storage/skill_store.rs

@@ -1,5 +1,4 @@
-use crate::Index;
-use crate::batch::Skill;
+use crate::{Index, batch::Skill};
 
 /// Dense Vec-backed store for per-agent skill state within a TimeSlice.
 ///
@@ -50,14 +49,17 @@ impl SkillStore {
         }
     }
 
+    #[allow(dead_code)]
     pub fn contains(&self, idx: Index) -> bool {
         idx.0 < self.present.len() && self.present[idx.0]
     }
 
+    #[allow(dead_code)]
     pub fn len(&self) -> usize {
         self.n_present
     }
 
+    #[allow(dead_code)]
     pub fn is_empty(&self) -> bool {
         self.n_present == 0
     }