shiftRight

    pub fn shiftRight(r: *Managed, a: *const Managed, shift: usize) !void {
        if (a.len() <= shift / limb_bits) {
            // Shifting negative numbers converges to -1 instead of 0
            if (a.isPositive()) {
                r.metadata = 1;
                r.limbs[0] = 0;
            } else {
                r.metadata = 1;
                r.setSign(false);
                r.limbs[0] = 1;
            }
            return;
        }

        const aliased = limbsAliasDistinct(r, a);
        const needed = a.len() - (shift / limb_bits);
        try r.ensureAliasAwareCapacity(needed, aliased);
        var m = r.toMutable();
        m.shiftRight(a.toConst(), shift);
        r.setMetadata(m.positive, m.len);
    }