docs: public MutableRoaringBitmap toMutableRoaringBitmap() {
      MutableRoaringBitmap c = new MutableRoaringBitmap();
      MappeableContainerPointer mcp = highLowContainer.getContainerPointer();
      while (mcp.hasContainer()) {
        c.getMappeableRoaringArray().appendCopy(mcp.key(), mcp.getContainer());
        mcp.advance();
      }
      return c;
    }