Add comprehensive telemetry system for Node.js SQL driver

Implements a complete telemetry system following the JDBC driver pattern:

Core Components:
- TelemetryEventEmitter: Event-based telemetry emission using Node.js EventEmitter
- MetricsAggregator: Per-statement aggregation with batch processing and periodic flushing
- DatabricksTelemetryExporter: HTTP export to Databricks telemetry endpoints with retry logic
- FeatureFlagCache: Per-host feature flag caching with reference counting
- CircuitBreaker: Per-host endpoint protection with OPEN/HALF_OPEN/CLOSED states
- ExceptionClassifier: Terminal vs retryable exception classification
- TelemetryClient/Provider: Per-host HTTP client management with reference counting

Integration:
- Integrated into DBSQLClient with per-connection lifecycle management
- Event emissions at key driver operations: connection.open, statement.start/complete, cloudfetch.chunk, error
- Feature flag driven with runtime override support via ConnectionOptions
- All telemetry errors swallowed and logged at debug level only
- Zero impact on driver operations when telemetry fails or is disabled

Testing:
- 226 comprehensive unit and integration tests
- 97.76% line coverage, 90.59% branch coverage, 100% function coverage
- Tests verify exception swallowing, debug-only logging, reference counting, circuit breaker behavior

Configuration:
- telemetryEnabled: boolean (default: false, feature flag driven)
- telemetryBatchSize: number (default: 100)
- telemetryFlushIntervalMs: number (default: 5000)
- telemetryRetryMaxAttempts: number (default: 3)

See docs/TELEMETRY.md for complete documentation.

Author: samikshya-db

README.md

@@ -51,6 +51,53 @@ client
   });
 ```
 
+## Telemetry
+
+The Databricks SQL Driver for Node.js includes an **opt-in telemetry system** that collects driver usage metrics and performance data to help improve the driver. Telemetry is **disabled by default** and follows a **privacy-first design**.
+
+### Key Features
+
+- **Privacy-first**: No SQL queries, results, or sensitive data is ever collected
+- **Opt-in**: Controlled by server-side feature flag (disabled by default)
+- **Non-blocking**: All telemetry operations are asynchronous and never impact your queries
+- **Resilient**: Circuit breaker protection prevents telemetry failures from affecting your application
+
+### What Data is Collected?
+
+When enabled, the driver collects:
+
+- ✅ Driver version and configuration settings
+- ✅ Query performance metrics (latency, chunk counts, bytes downloaded)
+- ✅ Error types and status codes
+- ✅ Feature usage (CloudFetch, Arrow format, compression)
+
+**Never collected**:
+
+- ❌ SQL query text
+- ❌ Query results or data values
+- ❌ Table/column names or schema information
+- ❌ User credentials or personal information
+
+### Configuration
+
+To enable or disable telemetry explicitly:
+
+```javascript
+const client = new DBSQLClient({
+  telemetryEnabled: true,  // Enable telemetry (default: false)
+});
+
+// Or override per connection:
+await client.connect({
+  host: '********.databricks.com',
+  path: '/sql/2.0/warehouses/****************',
+  token: 'dapi********************************',
+  telemetryEnabled: false,  // Disable for this connection
+});
+```
+
+For detailed documentation including configuration options, event types, troubleshooting, and privacy details, see [docs/TELEMETRY.md](docs/TELEMETRY.md).
+
 ## Run Tests
 
 ### Unit tests