Fix telemetry and feature flag implementation

- Fix event listener names: use 'connection.open' not 'telemetry.connection.open'
- Fix feature flag endpoint: use NODEJS client type instead of OSS_NODEJS
- Fix telemetry endpoints: use /telemetry-ext and /telemetry-unauth (not /api/2.0/sql/...)
- Update telemetry payload to match proto: use system_configuration with snake_case fields
- Add URL utility to handle hosts with or without protocol
- Add telemetryBatchSize and telemetryAuthenticatedExport config options
- Remove debug statements and temporary feature flag override

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: samikshya-db

lib/DBSQLClient.ts

@@ -290,6 +290,7 @@ export default class DBSQLClient extends EventEmitter implements IDBSQLClient, I
 
       // Check if telemetry enabled via feature flag
       const enabled = await this.featureFlagCache.isTelemetryEnabled(this.host);
+
       if (!enabled) {
         this.logger.log(LogLevel.debug, 'Telemetry disabled via feature flag');
         return;