do IO on a different thread
I do editing over SSH, and the only editor that can handle this is vscode. The reason for this is that most editors do IO on the same thread, and when the latency is high the process locks up while doing IO.
It is still really nice to have visual feedback of the save in progress, and I do want it to use fsync. As it is still using POSIX over the network there are excessive round-trips, but fixing that is not as important as making it possible.