Async user refreshing

Stale user refreshing should be done async to prevent blocking of rendering activities

Blocking rendering of an activity to fetch the latest profile of a user could mean waiting until the HTTP request times out. We should not block to return the absolute latest version of a User just because the last refresh was >24hrs ago. This could mean that e.g., the user's nickname and avatar could change between seeing the post on your timeline and opening up the thread, but the responsiveness should improve.

I think this is going to be most noticeable when you pull up activities of users you don't normally encounter on your instance, such as when viewing search results.