Add abstraction for upvoting/downvoting "in advance"

[ShadowJonathan]

Inspired by https://github.com/buresdv/Mlem/issues/115, I'd like for there to be a struct that'll hold the "actual count" together with the "virtual count", the "virtual" count being updated with user action, and then it kicking off a process to update the API to reflect this status.

This way, we don't need to fiddle with the API response to mock/trick the frontend into thinking it is the actual class, and also have a struct that will automatically debounce/adjust the voting status according to the user selection, and update the "upvoted" state back to the previous one when it fails, cascading through to the frontend.