Simplify runner::Runner::run

[sayanarijit]

The runner::Runner::run method is quite complicated and deals with a lot of variables.
This can be simplified by consolidating the variables into one or multiple structs.

[dtomvan]

The current implementation is also not very flexible (in the code). For example, I am trying to write a test for keybindings. I don't want the whole UI to show up, so I use an App and call handle_task on it. There is one problem, though. The App doesn't actually "handle" most tasks. It just enqueues it, for a Runner to use. Why not move the big match statement in app.rs (or use something like ExternalMsg::handle and let it match on self)? Runner handles the messages in a blocking fashion anyways.

[sayanarijit]

I wanted to keep App free of references. App should be an owned, serializable object. On the other hand, we have non-serializable objects like the terminal, channels, Lua VM etc. Runner::run is the place where they all interact with each other, without getting mixed up.

All I can think of is how to identify different objects in the Runner::run scope, and try to group them together in structs or functions, defined somewhere outside the run function, so that run doesn't take that much space. Unfortunately, I don't see how we can reduce complexity by moving the match statement somewhere else. But of course, if you have something in mind, you can raise a PR. Or maybe a stripped down version of xplr as demo.

[sayanarijit]

As for the keybindings, I agree it's a bit of a challenge to test. Need to steal ideas from other tui projects.