public PartitionAndNodeGroup splitCount(AtomicInteger splitCount) {
    this.splitCount = splitCount;
    return this;
  }
This is a group of the partitions and nodes of the mixed-format table, it can plan different
nodes and different partitions into different {@link MixedFormatSplit}.
amoro-format-mixed/amoro-mixed-flink/amoro-mixed-flink-common/src/main/java/org/apache/amoro/flink/read/PartitionAndNodeGroup.java