[5.4] nextDue for Schedule Event

[decadence]

Added a wrapper that allows find out when the next Carbon time Event will run.
For example this allows you to list events and their next run time in schedule method for debug:

protected function schedule(Schedule $schedule)
{
    $schedule->command('inspire')->yearly()->name("Inspire");

    foreach ($schedule->events() as $event) {
        echo $event->description . " will run next time at " . $event->nextDue()->toDateTimeString() . "\n";
    }
}