Function launch 

pub async fn launch<F, P>(_f: F, args: P) -> F::Output
where
    F: DeviceFn<P>,
    P: DeviceSend,

Launches a device function. Takes F by value so callers can pass the snake_case const emitted by #[device] (launch(my_fn, args)) rather than turbofishing the generated PascalCase unit struct (<MyFn as DeviceFn<_>>::execute(args)). The value is discarded; only its type drives trait dispatch.