shiftOnly

pub fn shiftOnly(self: Mod) bool {
        if (self == .none) return false;
        const lsh = @intFromEnum(Mod.lshift);
        const rsh = @intFromEnum(Mod.rshift);
        const mask = lsh | rsh;
        const input = @intFromEnum(self);
        return (input & mask) == input;
    }