feat: add state change events and callbacks (#798)

main/application.h

@@ -23,6 +23,7 @@
 #include "audio_processor.h"
 #include "wake_word.h"
 #include "audio_debugger.h"
+#include "device_state_event.h"
 
 #define SCHEDULE_EVENT (1 << 0)
 #define SEND_AUDIO_EVENT (1 << 1)
@@ -34,20 +35,6 @@ enum AecMode {
     kAecOnServerSide,
 };
 
-enum DeviceState {
-    kDeviceStateUnknown,
-    kDeviceStateStarting,
-    kDeviceStateWifiConfiguring,
-    kDeviceStateIdle,
-    kDeviceStateConnecting,
-    kDeviceStateListening,
-    kDeviceStateSpeaking,
-    kDeviceStateUpgrading,
-    kDeviceStateActivating,
-    kDeviceStateAudioTesting,
-    kDeviceStateFatalError
-};
-
 #define OPUS_FRAME_DURATION_MS 60
 #define MAX_AUDIO_PACKETS_IN_QUEUE (2400 / OPUS_FRAME_DURATION_MS)
 #define AUDIO_TESTING_MAX_DURATION_MS 10000