offload downloading images for the search to separate thread

[nednoodlehead]

not sure if this requires another full unbounded sender setup (with associated SenderSent message) or if there is some way we can have like a generic offload thread that we can make an enum for, and subscription::batch the types we give it (like the Download example in iced repo) and we have all of the stuff we say "lets offload it to another thread."

we can also offload:
database functions (delete, update..)
file system operations (like removing the temp dir)
downloading thumbnails for videos (will speed up the video download by like 1% lol)