Get the resources behind one PageSpeed issue on a page

The item-level detail for a single Lighthouse check on a single page: exactly which images, scripts, stylesheets or requests are at fault, each with its own wasted bytes or milliseconds. This is the 'what do I actually change' layer. Use page_speed_issues first to find the check and which pages it affects (affectedUrls), then call this per page. Read-only.