Function sample_single_excluding_rejection 

pub fn sample_single_excluding_rejection<'a, R, T, E>(
    rng: &mut R,
    slice: &'a [T],
    excluded: E,
) -> Option<&'a T>
where
    R: Rng,
    T: PartialEq,
    E: Borrow<T>,

Rejection-sampling implementation of sample_single_excluding. Picks a uniform index, accepts if not equal to excluded. Wins at n >= 4 and is essentially constant time when excluded appears 0 or 1 times. Falls through to sample_single_excluding_iteration after at most 16 consecutive matches (or n, whichever is smaller), which also returns None when every element matches. Exposed so benchmarks can compare strategies directly.