docs: public static MutableRoaringBitmap or(ImmutableRoaringBitmap... bitmaps) {
      SortedMap<Short, List<MappeableContainer>> grouped = groupByKey(bitmaps);
      short[] keys = new short[grouped.size()];
      MappeableContainer[] values = new MappeableContainer[grouped.size()];
      List<List<MappeableContainer>> slices = new ArrayList<>(grouped.size());
      int i = 0;
      for (Map.Entry<Short, List<MappeableContainer>> 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 MutableRoaringBitmap(new MutableRoaringArray(keys, values, i));
    }