Update processor to adapt for deadlines set change

- Processor dequeues tasks only when it's available to process
- Processor retries a task when its context's Done channel is closed

internal/base/base.go

@@ -267,7 +267,7 @@ func (c *Cancelations) GetAll() []context.CancelFunc {
 type Broker interface {
 	Enqueue(msg *TaskMessage) error
 	EnqueueUnique(msg *TaskMessage, ttl time.Duration) error
-	Dequeue(qnames ...string) (*TaskMessage, int, error)
+	Dequeue(qnames ...string) (*TaskMessage, time.Time, error)
 	Done(msg *TaskMessage) error
 	Requeue(msg *TaskMessage) error
 	Schedule(msg *TaskMessage, processAt time.Time) error