add java doc

Author: xx789633

fluss-lake/fluss-lake-iceberg/src/main/java/com/alibaba/fluss/lake/iceberg/tiering/writer/DeltaTaskWriter.java

@@ -37,6 +37,7 @@
 
 import java.util.List;
 
+/** A {@link RecordWriter} to write to Iceberg's primary-key table. */
 public class DeltaTaskWriter extends RecordWriter {
 
     public DeltaTaskWriter(

fluss-lake/fluss-lake-iceberg/src/main/java/com/alibaba/fluss/lake/iceberg/tiering/writer/GenericTaskDeltaWriter.java

@@ -30,6 +30,7 @@
 
 import java.io.IOException;
 
+/** A generic task equality delta writer. * */
 class GenericTaskDeltaWriter extends BaseTaskWriter<Record> {
     private final GenericEqualityDeltaWriter deltaWriter;