The easy-parallel crate spawned new threads on each call, which was resulting in way too many threads.
Co-Authored-By: Brooks Swinnerton <934497+bswinnerton@users.noreply.github.com>
I don't actually think it was correct to allow the future to borrow a mutable app reference. I went back to passing a wrapper around the refcell to async tests. They'll be a bit more annoying to write but also totally safe.
Also, eliminate the background spawning methods. We can spawn futures
on the executor and then spawn those on the app if we need to wait for
the result of running one.
