Prioritize federation to directly referenced instances

[BenLubar]

Pitch

Interacting with a user in a way that would send a notification (@-mentioning them, boosting their toot, etc.) should prioritize sending the ActivityPub object to their instance before other subscribing instances.

Motivation

Representative screenshot of Sidekiq a few minutes after I woke up this morning:

My instance is on my home internet and therefore shares 1.5Mbps of upload bandwidth with everyone in my house. For most things, I'm able to get around this with aggressive proxy caching, but replies to toots routinely take multiple minutes to get sent to the user I'm replying to.