@Override
  protected MixedFormatSplitState initializedState(MixedFormatSplit split) {
    return new MixedFormatSplitState(split);
  }
SourceEvents may be received before this#pollNext.
amoro-format-mixed/amoro-mixed-flink/amoro-mixed-flink-common/src/main/java/org/apache/amoro/flink/read/hybrid/reader/MixedFormatSourceReader.java