**feat(core, storage, tests): add service-level statistics tracking and storage adapter enhancements**

- **Core**: Enhanced `getStatistics` function to support `service` and `service[]` filters, enabling statistics breakdown by service. Modified return structure to include `serviceBreakdown` for detailed insights.
- **Storage**: Implemented a new `BaseStorageAdapter` abstract class to centralize statistics-related functionality, such as incrementing/decrementing counters and updating HNSW index size. Refactored all storage adapters (`FileSystemStorage`, `S3CompatibleStorage`, `MemoryStorage`, `OPFSStorage`) to extend `BaseStorageAdapter`, ensuring consistent statistics tracking.
- **Tests**: Added new test cases in `statistics.test.ts` to validate service-level statistics tracking, breakdown accuracy, and multi-service filtering.

**Purpose**: Improve insight into data trends by tracking service-specific usage in statistics. Enhance maintainability and consistency through storage adapter centralization and robust testing.

src/utils/statistics.ts

@@ -9,21 +9,34 @@ import { BrainyData } from '../brainyData.js'
  * This function provides access to statistics at the root level of the library
  * 
  * @param instance A BrainyData instance to get statistics from
+ * @param options Additional options for retrieving statistics
  * @returns Object containing counts of nouns, verbs, metadata entries, and HNSW index size
  * @throws Error if the instance is not provided or if statistics retrieval fails
  */
-export async function getStatistics(instance: BrainyData): Promise<{
+export async function getStatistics(
+    instance: BrainyData,
+    options: {
+        service?: string | string[] // Filter statistics by service(s)
+    } = {}
+): Promise<{
     nounCount: number
     verbCount: number
     metadataCount: number
     hnswIndexSize: number
+    serviceBreakdown?: {
+        [service: string]: {
+            nounCount: number
+            verbCount: number
+            metadataCount: number
+        }
+    }
 }> {
     if (!instance) {
         throw new Error('BrainyData instance must be provided to getStatistics')
     }
     
     try {
-        return await instance.getStatistics()
+        return await instance.getStatistics(options)
     } catch (error) {
         console.error('Failed to get statistics:', error)
         throw new Error(`Failed to get statistics: ${error}`)