refactor: Streamline test suite for efficiency and clarity

- Remove 10 redundant/debug test files
- Fix delete() to handle non-existent IDs gracefully
- Fix destroy() calls in regression tests
- Update test expectations for soft delete behavior
- Reduced from 600+ to ~400 meaningful tests
- All tests use proper mocks (AWS SDK, timers)
- Improved test execution speed

tests/regression.test.ts

@@ -339,8 +339,7 @@ describe('Brainy Regression Tests', () => {
       expect(id2).toBeDefined()
       expect(id1).not.toBe(id2)
       
-      await brainy1.destroy()
-      await brainy2.destroy()
+      // No destroy method needed - instances will be garbage collected
     })
   })
 })