@Override
  public boolean offer(T item) {
    return offer(item, 1);
  }
Algorithm: <i>Space-Saving</i>

@param item stream element (<i>e</i>)
@return false if item was already in the stream summary, true otherwise
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/execution/operator/source/relational/aggregation/approximate/StreamSummary.java