protected Table getTableStore() {
      if (tableStore == null) {
        if (table.isKeyedTable()) {
          if (onChangeStore) {
            tableStore = table.asKeyedTable().changeTable();
          } else {
            tableStore = table.asKeyedTable().baseTable();
          }
        } else {
          tableStore = table.asUnkeyedTable();
        }
      }
      return tableStore;
    }
Abstract implementation of {@link PendingUpdate}, adding mixed-format logics like tracing and
watermark generating for iceberg operations.

@param <T> Java class of changes from this update; returned by {@link #apply} for validation.
amoro-format-iceberg/src/main/java/org/apache/amoro/op/MixedUpdate.java