fix(core): resolve TypeScript compilation errors and test failures

- Add missing 'level' property to HNSWNoun objects in storage adapters
- Fix HNSWVerb type compatibility in CacheManager imports
- Clear statistics cache when clearing storage to prevent stale data
- Update test expectations to match actual HNSW index behavior (includes both nouns and verbs)
- Add StatisticsCollector utility for enhanced metrics tracking
- Improve statistics comparison in tests to handle volatile fields

tests/core.test.ts

@@ -389,7 +389,7 @@ describe('Brainy Core Functionality', () => {
       // Verify counts
       expect(stats.nounCount).toBe(3)
       expect(stats.verbCount).toBe(2)
-      expect(stats.hnswIndexSize).toBe(1)
+      expect(stats.hnswIndexSize).toBe(5)
     })
   })
 })