**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/storage/adapters/baseStorageAdapter.ts

@@ -0,0 +1,158 @@
+/**
+ * Base Storage Adapter
+ * Provides common functionality for all storage adapters, including statistics tracking
+ */
+
+import { StatisticsData, StorageAdapter } from '../../coreTypes.js'
+
+/**
+ * Base class for storage adapters that implements statistics tracking
+ */
+export abstract class BaseStorageAdapter implements StorageAdapter {
+  // Abstract methods that must be implemented by subclasses
+  abstract init(): Promise<void>
+  abstract saveNoun(noun: any): Promise<void>
+  abstract getNoun(id: string): Promise<any | null>
+  abstract getAllNouns(): Promise<any[]>
+  abstract getNounsByNounType(nounType: string): Promise<any[]>
+  abstract deleteNoun(id: string): Promise<void>
+  abstract saveVerb(verb: any): Promise<void>
+  abstract getVerb(id: string): Promise<any | null>
+  abstract getAllVerbs(): Promise<any[]>
+  abstract getVerbsBySource(sourceId: string): Promise<any[]>
+  abstract getVerbsByTarget(targetId: string): Promise<any[]>
+  abstract getVerbsByType(type: string): Promise<any[]>
+  abstract deleteVerb(id: string): Promise<void>
+  abstract saveMetadata(id: string, metadata: any): Promise<void>
+  abstract getMetadata(id: string): Promise<any | null>
+  abstract clear(): Promise<void>
+  abstract getStorageStatus(): Promise<{
+    type: string
+    used: number
+    quota: number | null
+    details?: Record<string, any>
+  }>
+
+  // Statistics-specific methods
+  protected abstract saveStatisticsData(statistics: StatisticsData): Promise<void>
+  protected abstract getStatisticsData(): Promise<StatisticsData | null>
+
+  /**
+   * Save statistics data
+   * @param statistics The statistics data to save
+   */
+  async saveStatistics(statistics: StatisticsData): Promise<void> {
+    await this.saveStatisticsData(statistics)
+  }
+
+  /**
+   * Get statistics data
+   * @returns Promise that resolves to the statistics data
+   */
+  async getStatistics(): Promise<StatisticsData | null> {
+    return await this.getStatisticsData()
+  }
+
+  /**
+   * Increment a statistic counter
+   * @param type The type of statistic to increment ('noun', 'verb', 'metadata')
+   * @param service The service that inserted the data
+   * @param amount The amount to increment by (default: 1)
+   */
+  async incrementStatistic(
+    type: 'noun' | 'verb' | 'metadata',
+    service: string,
+    amount: number = 1
+  ): Promise<void> {
+    // Get current statistics or create default if not exists
+    let statistics = await this.getStatisticsData()
+    if (!statistics) {
+      statistics = this.createDefaultStatistics()
+    }
+
+    // Increment the appropriate counter
+    const counterMap = {
+      noun: statistics.nounCount,
+      verb: statistics.verbCount,
+      metadata: statistics.metadataCount
+    }
+
+    const counter = counterMap[type]
+    counter[service] = (counter[service] || 0) + amount
+
+    // Update timestamp
+    statistics.lastUpdated = new Date().toISOString()
+
+    // Save updated statistics
+    await this.saveStatisticsData(statistics)
+  }
+
+  /**
+   * Decrement a statistic counter
+   * @param type The type of statistic to decrement ('noun', 'verb', 'metadata')
+   * @param service The service that inserted the data
+   * @param amount The amount to decrement by (default: 1)
+   */
+  async decrementStatistic(
+    type: 'noun' | 'verb' | 'metadata',
+    service: string,
+    amount: number = 1
+  ): Promise<void> {
+    // Get current statistics or create default if not exists
+    let statistics = await this.getStatisticsData()
+    if (!statistics) {
+      statistics = this.createDefaultStatistics()
+    }
+
+    // Decrement the appropriate counter
+    const counterMap = {
+      noun: statistics.nounCount,
+      verb: statistics.verbCount,
+      metadata: statistics.metadataCount
+    }
+
+    const counter = counterMap[type]
+    counter[service] = Math.max(0, (counter[service] || 0) - amount)
+
+    // Update timestamp
+    statistics.lastUpdated = new Date().toISOString()
+
+    // Save updated statistics
+    await this.saveStatisticsData(statistics)
+  }
+
+  /**
+   * Update the HNSW index size statistic
+   * @param size The new size of the HNSW index
+   */
+  async updateHnswIndexSize(size: number): Promise<void> {
+    // Get current statistics or create default if not exists
+    let statistics = await this.getStatisticsData()
+    if (!statistics) {
+      statistics = this.createDefaultStatistics()
+    }
+
+    // Update HNSW index size
+    statistics.hnswIndexSize = size
+
+    // Update timestamp
+    statistics.lastUpdated = new Date().toISOString()
+
+    // Save updated statistics
+    await this.saveStatisticsData(statistics)
+  }
+
+  /**
+   * Create default statistics data
+   * @returns Default statistics data
+   */
+  protected createDefaultStatistics(): StatisticsData {
+    return {
+      nounCount: {},
+      verbCount: {},
+      metadataCount: {},
+      hnswIndexSize: 0,
+      lastUpdated: new Date().toISOString()
+    }
+  }
+}