Queue.WorkableJobSourceA workable job can process a job instance that is persisted. We can not store the job directly because of the polymorphic type ('a Job.t).
type t = {name : string;with_context : Core.Ctx.t -> Core.Ctx.t;work : Core.Ctx.t -> input:string option -> (unit, string) Result.t Lwt.t;failed : Core.Ctx.t -> (unit, string) Result.t Lwt.t;max_tries : int;retry_delay : Utils.Time.duration;}