docs: public static CallOptions withAnnotation(CallOptions callOptions, Object annotation) {
      Collection<Object> existingAnnotations = callOptions.getOption(CRONET_ANNOTATIONS_KEY);
      ArrayList<Object> newAnnotations;
      if (existingAnnotations == null) {
        newAnnotations = new ArrayList<>();
      } else {
        newAnnotations = new ArrayList<>(existingAnnotations);
      }
      newAnnotations.add(annotation);
      return callOptions.withOption(
          CronetCallOptions.CRONET_ANNOTATIONS_KEY, Collections.unmodifiableList(newAnnotations));
    }