Add telemetry testing and documentation

This is part 7 of 7 in the telemetry implementation stack - FINAL LAYER.

Documentation:
- README.md: Add telemetry overview section
- docs/TELEMETRY.md: Comprehensive telemetry documentation
- spec/telemetry-design.md: Detailed design document
- spec/telemetry-sprint-plan.md: Implementation plan
- spec/telemetry-test-completion-summary.md: Test coverage report

README.md Updates:
- Added telemetry overview section
- Configuration examples with all 7 options
- Privacy-first design highlights
- Link to detailed TELEMETRY.md

TELEMETRY.md - Complete User Guide:
- Overview and benefits
- Privacy-first design (what is/isn't collected)
- Configuration guide with examples
- Event types with JSON schemas
- Feature control (server-side flag + client override)
- Architecture overview
- Troubleshooting guide
- Privacy & compliance (GDPR, CCPA, SOC 2)
- Performance impact analysis
- FAQ (12 common questions)

Design Document (telemetry-design.md):
- Complete system architecture
- Component specifications
- Data flow diagrams
- Error handling requirements
- Testing strategy
- Implementation phases

Test Coverage Summary:
- 226 telemetry tests passing
- 97.76% line coverage
- 90.59% branch coverage
- 100% function coverage
- Critical requirements verified

Test Breakdown by Component:
- ExceptionClassifier: 51 tests (100% coverage)
- CircuitBreaker: 32 tests (100% functions)
- FeatureFlagCache: 29 tests (100% functions)
- TelemetryEventEmitter: 31 tests (100% functions)
- TelemetryClient: 31 tests (100% functions)
- TelemetryClientProvider: 31 tests (100% functions)
- MetricsAggregator: 32 tests (94% lines, 82% branches)
- DatabricksTelemetryExporter: 24 tests (96% statements)
- Integration: 11 E2E tests

Critical Test Verification:
✅ All exceptions swallowed (no propagation)
✅ Debug-only logging (no warn/error)
✅ No console logging
✅ Driver works when telemetry fails
✅ Reference counting correct
✅ Circuit breaker behavior correct

This completes the 7-layer telemetry implementation stack!

Signed-off-by: samikshya-chand_data <samikshya.chand@databricks.com>

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