Support Unit Tuple

[Max-Cao]

In Rust, we have () as the unit tuple
In C++, we have std::tuple<>
why sus::Tuple cant inst a unit tuple

[danakj]

Good observation, I think I just never tried. It should support it.

[Max-Cao]

Yes. And I see there's OkVoid in sus::result, but a unit tuple is more versatile