Get the status of an async one-call LipDub2 generation.

Args:
    tracking_id: The tracking id returned by POST /v1/renders (async case)

Returns:
    Dict containing 'data' ({tracking_id, status, generate_id, failure_reason}). `generate_id` is
    set once the render is dispatched; use it with GET /v1/renders/{generate_id}/download.