Function pack_bits_le

pub fn pack_bits_le<R, Var, I>(iter: I) -> R
where
    R: PrimeCharacteristicRing,
    Var: Into<R> + Clone,
    I: DoubleEndedIterator<Item = Var>,

Pack a collection of bits into a number.

Given vec = [v_0, v_1, ..., v_n] returns v_0 + 2v_1 + ... + 2^n v_n