Upscale an image: the same picture at a higher resolution, up to 4x, with the result capped at 2048px on its longest side. The source image (URL or base64) must be below 2048px on its longest side; a larger one is rejected with HTTP 400. The job result is a single image result with a url (not an array). The image is uploaded and validated, and an image larger than 15MB is rejected with HTTP 400. Credits are held when the job is accepted and refunded if it fails or is cancelled. Use upscaleImage to raise the resolution of an image you already have; createImage and editImage make new or changed images instead. Pass an optional request_id to tag the result so you can retrieve it later via listGenerations (type image). Requires an API key (user scope). The call returns 202 with a job id - poll `GET /assets/jobs/{id}`, honouring poll_after_ms or long-polling with wait=30, until status is succeeded; its result field is exactly the response documented for this operation. Synchronous responses are deprecated but still supported: pass `async: false` to block until the result is ready and receive it as the response body. Synchronous calls run on the same queue: the response carries an X-Ludo-Job-Id header, and a job still running after 15 minutes comes back as 202 with the job instead of an error. Each account may have up to 50 generations queued or running at once via the API; a request beyond that returns 429 (code PENDING_JOBS_LIMIT).