Add PlanNodeType enum value for tsfile object piece. (#17431)

This reserves a dedicated plan node type code for LOAD_TSFILE_OBJECT_PIECE to support downstream planning and serialization logic.

Author: luoluoyuyu

iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/planner/plan/node/PlanNodeType.java

@@ -276,6 +276,7 @@ public enum PlanNodeType {
   // 100 - 106 are occupied
   SHOW_DISK_USAGE((short) 107),
   TREE_COLLECT((short) 108),
+  LOAD_TSFILE_OBJECT_PIECE((short) 109),
 
   CREATE_OR_UPDATE_TABLE_DEVICE((short) 902),
   TABLE_DEVICE_QUERY_SCAN((short) 903),