Allow functions returning unit in use_effect

[WorldSEnder]

Discussed in #2843

^{Originally posted by arniu August 25, 2022}
sample

trait TearDown: Sized {
    fn tear_down(self) {}
}

impl TearDown for () {}

impl<F: FnOnce()> TearDown for F {
    fn tear_down(self) {
        self()
    }
}

fn use_effect<F, R>(f: F)
where
    F: Fn() -> R,
    R: TearDown,
{ todo!() }