Ensure statement_type always populated in telemetry

Fix issue where statement_type was null in telemetry payloads.

Changes:
- mapOperationTypeToTelemetryType() now always returns a string,
  defaulting to 'TYPE_UNSPECIFIED' when operationType is undefined
- statement_type always included in sql_operation telemetry log

This ensures that even if the Thrift operationHandle doesn't have
operationType set, the telemetry will include 'TYPE_UNSPECIFIED'
instead of null.

Root cause: operationHandle.operationType from Thrift response can
be undefined, resulting in null statement_type in telemetry logs.

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

Author: samikshya-db

lib/telemetry/DatabricksTelemetryExporter.ts

@@ -329,7 +329,7 @@ export default class DatabricksTelemetryExporter {
       // Only create sql_operation if we have any fields to include
       if (metric.operationType || metric.compressed !== undefined || metric.resultFormat || metric.chunkCount) {
         log.entry.sql_driver_log.sql_operation = {
-          ...(metric.operationType && { statement_type: metric.operationType }),
+          statement_type: metric.operationType,
           ...(metric.compressed !== undefined && { is_compressed: metric.compressed }),
           ...(metric.resultFormat && { execution_result: metric.resultFormat }),
         };

lib/telemetry/telemetryTypeMappers.ts

@@ -18,10 +18,11 @@ import { TOperationType, TSparkRowSetType } from '../../thrift/TCLIService_types
 
 /**
  * Map Thrift TOperationType to telemetry Operation.Type enum string.
+ * Returns 'TYPE_UNSPECIFIED' if operationType is undefined or unknown.
  */
-export function mapOperationTypeToTelemetryType(operationType?: TOperationType): string | undefined {
+export function mapOperationTypeToTelemetryType(operationType?: TOperationType): string {
   if (operationType === undefined) {
-    return undefined;
+    return 'TYPE_UNSPECIFIED';
   }
 
   switch (operationType) {