Default no-op store. Assigns VM-local monotonic IDs but does not persist. Jobs are lost on VM restart.
Note on get_job/1
This function intentionally returns {:error, :not_found} for every call.
The Memory store does not retain job state — it only generates IDs on
insert_job/1. The authoritative source for in-memory jobs is the
Core.Workers.JobQueue GenServer, which holds the full %Job{} structs
in its state map.