docs: public List<List<Metric>> getObservations() {
      List<List<Metric>> builder = new ArrayList<>();
      int pos = next;
      for (List<Metric> ignored : observations) {
        if (observations[pos] != null) {
          builder.add(observations[pos]);
        }
        pos = (pos + 1) % observations.length;
      }
      return Collections.unmodifiableList(builder);
    }