In-process job buffer with background polling from job-manager.

Jobs are claimed from the database in batches and held in a
LinkedBlockingQueue until a worker calls take-job!. The poll loop runs
as a daemon thread and automatically refetches when the buffer depth
drops below the configured threshold.

Local in-process job queue with background polling from job-manager.

The queue batches job claims from the database into a local buffer and
distributes them to workers via take-job!. A background daemon thread
polls job-manager continuously, refetching whenever the buffer depth
drops below the configured threshold.

Typical usage (worker-pool calls create-queue once per pool):

  (def q (-> (queue/create-queue sys worker-id {:size 50})
             queue/start!))

  ;; Worker thread loop
  (when-let [job (queue/take-job! q 2000)]
    (try
      (execute job)
      (job-manager/complete-jobs sys (queue/worker-id q) [job] elapsed)
      (catch Exception e
        (job-manager/fail-jobs sys (queue/worker-id q)
                               [{:job job :error e}] elapsed))))

  ;; On shutdown
  (let [undispatched (queue/stop! q)]
    ;; undispatched jobs remain locked in DB; they will be recovered
    ;; by the ResetOverdueJobs rule after config.lock_timeout.

Malli schemas for queue component.