feat: Add pipewire backend

> only for testing current bmsound_wine implementation wine-side

hooks/audio/audio.h

@@ -11,6 +11,7 @@ namespace hooks::audio {
     enum class Backend {
         Asio,
         WaveOut,
+        Pipewire,
         None
     };
 
@@ -28,6 +29,8 @@ namespace hooks::audio {
             return Backend::Asio;
         } else if (_stricmp(value, "waveout") == 0) {
             return Backend::WaveOut;
+        } else if (_stricmp(value, "pipewire") == 0) {
+            return Backend::Pipewire;
         } else if (_stricmp(value, "none") == 0) {
             return Backend::None;
         }