Change architecture to controller-centered arch

struct PipewireConnection is now decoupled from any other components, another component (the controller)
can receive updates by registering a callback.

struct PipewireState has been refactored to a struct Controller.
It still keeps state and manages the view, but now also actively requests updates from the pipewire connection via callback.

Cargo.lock

@@ -583,6 +583,7 @@ dependencies = [
  "gtk4",
  "libspa",
  "log",
+ "once_cell",
  "pipewire",
 ]