Function bitonic_sort_by_key 

pub fn bitonic_sort_by_key<T: Clone>(
    data: &mut Vec<T>,
    key_fn: impl Fn(&T) -> u32,
)

Sort a VecTby theu32key returned bykey_fn`.

Padding uses sentinel key u32::MAX; after sorting, only the first orig_len elements (those with valid indices) are retained.