make interface of merge append action consistent

Author: ZENOTME

crates/iceberg/src/transaction/merge_append.rs

@@ -106,12 +106,9 @@ impl MergeAppendAction {
     }
 
     /// Add data files to the snapshot.
-    pub fn add_data_files(
-        &mut self,
-        data_files: impl IntoIterator<Item = DataFile>,
-    ) -> Result<&mut Self> {
+    pub fn add_data_files(mut self, data_files: impl IntoIterator<Item = DataFile>) -> Self {
         self.added_data_files.extend(data_files);
-        Ok(self)
+        self
     }
 }
 

crates/integration_tests/tests/shared_tests/merge_append_test.rs

@@ -173,10 +173,7 @@ async fn test_append_data_file() {
     // append data file with merge append, 4 data file will be merged to two manifest
     let data_file = write_new_data_file(&table).await;
     let tx = Transaction::new(&table);
-    let mut merge_append_action = tx.merge_append().unwrap();
-    merge_append_action
-        .add_data_files(data_file.clone())
-        .unwrap();
+    let merge_append_action = tx.merge_append().unwrap().add_data_files(data_file.clone());
     let tx = merge_append_action.apply(tx).unwrap();
     table = tx.commit(&rest_catalog).await.unwrap();
     // Check manifest file