Parallel streaming of progressive images

What this post added

Introduced a new feature for parallel streaming of progressive images by leveraging HTTP/2 prioritization. This technique dynamically re-prioritizes image data fragments: image headers are high priority for layout stability, minimum preview data is medium priority, and the remainder is low priority. This improves perceived image load time by up to 50% and allows pages to render sooner without additional data or JavaScript. The implementation is format-independent but most beneficial for JPEG and JPEG 2000. A custom `cf-priority-change` header is supported for experimentation with other resource types.