actix_web::web::Data, but with Rc instead of Arc.
This is useful when you have something like a config struct, which doesn't take up a whole lot of memory, but is also not small enough to copy all the time.
LocalData will allow you to have a local copy on each thread, which does not need
to be copied into handlers.
This is a fairly niche utility crate, so I'm not publishing it on crates for now.