docs: @SuppressWarnings("unchecked")
    public static <ObsT, SummaryT> Builder<ObsT, SummaryT> forSummarizer(
        final ObservationSummarizer<? super ObsT, ? extends SummaryT> observationSummarizer,
        int numSamples,
        final Random rng) {
      return new Builder<ObsT, SummaryT>(
          (ObservationSummarizer<ObsT, SummaryT>) observationSummarizer, numSamples, rng);
    }