default KeyedTable asKeyedTable() {
    throw new IllegalStateException("Not a keyed table");
  }
Returns this cast to {@link KeyedTable} if it is one

@return this cast to {@link KeyedTable} if it is one
@throws IllegalStateException if this is not a {@link KeyedTable}
amoro-format-iceberg/src/main/java/org/apache/amoro/table/MixedTable.java