Modify architecture to run pipewire loop in second thread.

The pipewire loop now runs without interruption in a second thread and communicates with
the GTK thread via a channel in each direction, instead of checking for events once a second and using callbacks.

This allows changes to appear instantly in the view, instead of having to wait.

src/view/mod.rs

@@ -13,7 +13,7 @@ use gtk::{
     glib::{self, clone},
     prelude::*,
 };
-use pipewire::port::Direction;
+use pipewire::spa::Direction;
 
 use crate::controller::MediaType;