default byte[] getEpicNoBytes() {
    return Longs.toByteArray(getEpicNo());
  }
The epic number indicates a batch of data in the log queue(e.g. Kafka), the EpicNo is similar
to the checkpoint id in the flink application.

@return epic number
amoro-format-iceberg/src/main/java/org/apache/amoro/log/LogData.java