Function stable_sort

src/fl/stl/algorithm.h:582–588

// Stable sort function with custom comparator (using merge sort)
template <typename Iterator, typename Compare>
void stable_sort(Iterator first, Iterator last, Compare comp) FL_NOEXCEPT {
    if (first == last || first + 1 == last) {
        return;  // Already sorted or empty
    }
    
    detail::mergesort_impl(first, last, comp);
}

// Stable sort function with default comparator
template <typename Iterator>