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/node.rs

@@ -1,7 +1,7 @@
 use super::graph_view::GraphView;
 
 use gtk::{glib, prelude::*, subclass::prelude::*, WidgetExt};
-use pipewire::port::Direction;
+use pipewire::spa::Direction;
 
 use std::{collections::HashMap, rc::Rc};