support/num_traits: AsPrimitive

[github-actions]

On 2023-08-28 @recmo wrote in 585c5ce “Merge pull request #298 from recmo/num-traits”:

AsPrimitive

    pow::Pow,
    sign::Unsigned,
    CheckedEuclid, Euclid, Inv, MulAdd, MulAddAssign, Num, NumCast,
};

// TODO: AsPrimitive

// Note. We can not implement `NumBytes` as it requires T to be `AsMut<[u8]>`.
// This is not safe for `Uint` when `BITS % 8 != 0`.

impl<const BITS: usize, const LIMBS: usize> Zero for Uint<BITS, LIMBS> {

From src/support/num_traits.rs:29

[moh-eulith]

Is there an efficient way to get the lowest N bits into u<N> (u8, u16, etc)? I can do u8 via byte(0), but that's about it.