Enable error variances of more than 16

[tlepoint]

The variance for sampling according to the centered binomial distribution is currently capped at 16:

pub fn sample_vec_cbd(vector_size: usize, variance: usize) -> Result<Vec<i64>, &'static str> {
	if !(1..=16).contains(&variance) {
		return Err("The variance should be between 1 and 16");
	}

It would be good to enable larger values.