fix: use public method instead of private operationDataMap property

- Replace storage.operationDataMap with storage.getAllOperationData()
- Fixes TypeScript compilation error about accessing private property

Author: ParidelPooya

packages/aws-durable-execution-sdk-js-testing/src/checkpoint-server/handlers/checkpoint-handlers.ts

@@ -105,7 +105,7 @@ export function processCheckpointDurableExecution(
     createCheckpointToken(input.CheckpointToken),
   );
 
-  validateCheckpointUpdates(updates, storage.operationDataMap);
+  validateCheckpointUpdates(updates, storage.getAllOperationData());
 
   storage.registerUpdates(updates);