`power_multiset`: `powerset` where repeated items don't produce repeated subsets

[Pr0methean]

It would be nice to have a version of the following as a convenient, efficient library function rather than having had to roll my own:

#[inline]
fn power_multiset<T: PartialEq + Ord + Copy>(multiset: &mut Vec<T>) -> Vec<Vec<T>> {
    let mut result = Vec::new();
    multiset.sort_unstable(); // Sort to handle duplicates more easily

    #[inline]
    fn generate_subsets<T: PartialEq + Copy>(
        current_subset: &mut Vec<T>,
        remaining_elements: &mut Vec<T>,
        all_subsets: &mut Vec<Vec<T>>,
    ) {
        // Add the current subset to the result
        all_subsets.push(current_subset.clone());

        if remaining_elements.is_empty() {
            return;
        }

        let mut i = 0;
        while i < remaining_elements.len() {
            let element = remaining_elements.remove(i);
            current_subset.push(element);

            generate_subsets(current_subset, remaining_elements, all_subsets);

            // Backtrack: add the element back and remove from current_subset
            current_subset.pop();
            remaining_elements.insert(i, element);

            // Skip duplicate elements to avoid redundant subsets
            while i < remaining_elements.len() && remaining_elements[i] == element {
                i += 1;
            }
        }
    }

    let mut current_subset = Vec::new();
    generate_subsets(&mut current_subset, multiset, &mut result);
    for subset in result.iter_mut() {
        subset.sort_unstable();
    }
    result.sort_unstable();
    result.dedup();
    result
}

    #[test]
    fn test_power_multiset() {
        let mut multiset = vec![2, 2, 3, 3, 5];
        let power_multiset = power_multiset(&mut multiset);
        println!("{:?}", power_multiset);
        assert_eq!(power_multiset.len(), 18);
        assert!(power_multiset.contains(&vec![]));
        assert!(power_multiset.contains(&vec![2]));
        assert!(power_multiset.contains(&vec![2, 2]));
        assert!(power_multiset.contains(&vec![3]));
        assert!(power_multiset.contains(&vec![2, 3]));
        assert!(power_multiset.contains(&vec![2, 2, 3]));
        assert!(power_multiset.contains(&vec![3, 3]));
        assert!(power_multiset.contains(&vec![2, 3, 3]));
        assert!(power_multiset.contains(&vec![2, 2, 3, 3]));
        assert!(power_multiset.contains(&vec![5]));
        assert!(power_multiset.contains(&vec![2, 5]));
        assert!(power_multiset.contains(&vec![2, 2, 5]));
        assert!(power_multiset.contains(&vec![3, 5]));
        assert!(power_multiset.contains(&vec![2, 3, 5]));
        assert!(power_multiset.contains(&vec![2, 2, 3, 5]));
        assert!(power_multiset.contains(&vec![3, 3, 5]));
        assert!(power_multiset.contains(&vec![2, 3, 3, 5]));
        assert!(power_multiset.contains(&vec![2, 2, 3, 3, 5]));
    }