Guard against stop() during loadAndPlaySpin await

After awaiting player.load(), check that stationId is still set before
proceeding to playback. If stop() ran during the suspension, clean up
the player instead of overwriting the .idle state.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: briankeane

Sources/PlayolaPlayer/Player/Streaming/StreamingStationPlayer.swift

@@ -174,6 +174,14 @@ final public class StreamingStationPlayer: ObservableObject {
     let player = getOrCreateSpinPlayer(for: spin)
 
     let result = await player.load(spin)
+
+    // Guard against stop() called during the await
+    guard stationId != nil else {
+      player.clear()
+      spinPlayers.removeValue(forKey: spin.id)
+      return
+    }
+
     switch result {
     case .success:
       let timing = spin.playbackTiming