docs: public static RoaringBitmap or(RoaringBitmap... bitmaps) {
      SortedMap<Short, List<Container>> grouped = groupByKey(bitmaps);
      short[] keys = new short[grouped.size()];
      Container[] values = new Container[grouped.size()];
      List<List<Container>> slices = new ArrayList<>(grouped.size());
      int i = 0;
      for (Map.Entry<Short, List<Container>> slice : grouped.entrySet()) {
        keys[i++] = slice.getKey();
        slices.add(slice.getValue());
      }
      IntStream.range(0, i)
               .parallel()
               .forEach(position -> values[position] = or(slices.get(position)));
      return new RoaringBitmap(new RoaringArray(keys, values, i));
    }