One-shot worker that pre-loads a detector's models at boot.

An ImagePipe instance starts it with the instance's detector and the classes from its :detector_warmup option. A configuration used without an instance, such as a mount configured in the router, needs the worker in the host's supervision tree:

{ImagePipe.Transform.Detector.Warmup, detector: :default}

:detector accepts :default (the bundled adapter, used when omitted), nil (no work), or a custom detector module, matching the plug option.

Failed warmup results are logged and retried with bounded exponential backoff. The worker then exits normally, so restart: :transient does not restart it. Unavailable detectors are skipped. It does not trap exits; shutdown during a download needs no cleanup.

Model loading runs in handle_continue/2, allowing start_link/1 to return without waiting for the download.