[FEATURE] - Dynamic duration

[babyfish-ct]

Add a function like SetNextDuration into Job, which can change the duration of the current job for next execution. the duration of the current job will be automatically reset after next execution.

For example

s, _ := NewScheduler()
defer func() { _ = s.Shutdown() }()

job, _ = s.NewJob(
	DurationJob(
	        // 1. Default behavior: Short waiting
		time.Second, 
	),
	NewTask(
		func() {
		    tasks := taskRepository.FetchBatch(100)
		    if len(tasks) == 0 {
		        // 2. Conditional behavior: Long waiting
		        job.SetNextDuration(time.Minute) 
		    }
		    taskExectuor.Execute(tasks)
		},
	),
)

That means：If there are some tasks, there is a short break (1 second) between each execution; If there are no tasks, there is a longer break between each execution (1 minute).