Fix crash with event watchers + handle SDL loop better + shut down more appropriately

src/frontend/KaizenGui.hpp

@@ -11,6 +11,7 @@ class KaizenGui final {
   gui::NativeWindow window;
 public:
   explicit KaizenGui() noexcept;
+  ~KaizenGui();
   double fpsCounter = -1.0;
   gui::MenuBar<true> menuBar;
   gui::MenuItem actionPause{"Pause", nullptr, false}, actionStop{"Stop", nullptr, false}, actionReset{"Reset", nullptr, false};
@@ -21,7 +22,7 @@ public:
   gui::PopupWindow about{"About Kaizen"};
   gui::StatusBar statusBar{};
   
-  int run();
+  void run();
   void LoadTAS(const std::string &path) const noexcept;
   void LoadROM(const std::string &path) noexcept;
 private: