public ReaderOutput<T> wrapOutput(ReaderOutput<T> output) {
    if (!(output instanceof SourceOutputWithWatermarks)) {
      return output;
    }
    return new MixedFormatReaderOutput<>(output);
  }
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