refactor(daemon): Consolidate PipeWire operations into a single background actor

Replaces the previous approach of spawning new PipeWire main loops and
awaiting a 100ms timeout for every `get_all_devices` call. Instead,
this introduces a `PipeWireManager` which maintains a single, persistent
background thread with a PipeWire main loop and registry listener. The
actor caches `AudioDevice`s and `Port`s continuously in a `HashMap`,
providing instantaneous responses to device queries via a channel.

This architectural change replaces `Sender<Terminate>` with a simple
`PwTerminator` drop-guard to manage the lifetimes of PipeWire objects
(virtual mic and links) via `PwCommand::DestroyObject` without creating
additional OS threads or PipeWire contexts.

Co-authored-by: google-labs-jules[bot] <161369871+google-labs-jules[bot]@users.noreply.github.com>

pwsp-daemon/src/main.rs

@@ -28,7 +28,10 @@ async fn main() -> Result<()> {
     }
 
     get_daemon_config(); // Initialize daemon config
-    create_virtual_mic()?;
+
+    // Virtual mic object must be kept alive by some variable until daemon exits
+    let _virtual_mic = create_virtual_mic().await?;
+
     if let Err(err) = get_audio_player().await {
         eprintln!("Failed to initialize audio player: {}", err);
     } // Initialize audio player