respects async/deferred link tags (CSS stylesheets with `rel="preload"`)

To Do: Ensure that link tag caching respects respects async/deferred CSS stylesheets

see here: https://web.dev/articles/defer-non-critical-css

Start by reading the repository's link-tag caching logic and the linked web.dev article on deferring non-critical CSS. Verify how CSS stylesheets using rel="preload" are handled, and consider the work complete when async or deferred stylesheets are cached consistently with ordinary stylesheets.

Written by the indexing model from the issue text.