Function `median_of_medians`

pub(in ::slice::sort::select) fn median_of_medians<T, F: FnMut(&T, &T) -> bool>(v: &mut [T], is_less: &mut F, k: usize)

Selection algorithm to select the k-th element from the slice in guaranteed O(n) time. This is essentially a quickselect that uses Tukey's Ninther for pivot selection