Scope.Task_handletype 'a scope := 'a tinto_scope task_handle consumes the task handle and turns it into the scope the task was spawned into.
val become_daemon :
'a t @ local unique ->
#('a scope * Await_kernel.Cancellation.t) @ localbecome_daemon task_handle consumes the task handle, turns the task it represents into a daemon task, and returns the scope the daemon task was spawned into, along with a cancellation token that is canceled once all non-daemon tasks exit.