ImageTaskDelegate

[kean]

Add ImageTaskDelegate to achieve complete feature-parity with completion-based APIs:

Loading an image and monitoring download progress:

func loadImage() async throws {
    let response = try await pipeline.image(for: "https://example.com/image.jpeg", delegate: self)
}

func imageTask(_ task: ImageTask, didUpdateProgress progress: (completed: Int64, total: Int64)) {
    print("Image task did update progress: \(progress)")
}

All ImageTaskDelegate methods are guaranteed to be called on the pipeline's callbackQueue (main queue, by default).