[nostalgia] Make core::shutdown return void and add GBA implementation

src/nostalgia/core/context.hpp

@@ -56,7 +56,7 @@ class Context {
 	                                 const ox::FileAddress &tilesheetPath,
 	                                 const ox::FileAddress &palettePath) noexcept;
 	friend ox::Error run(Context *ctx) noexcept;
-	friend ox::Error shutdown(Context *ctx) noexcept;
+	friend void shutdown(Context *ctx) noexcept;
 	friend ox::Result<ox::UniquePtr<Context>> init(ox::UniquePtr<ox::FileSystem> fs, const char *appName) noexcept;
 	friend ox::String getClipboardText(Context *ctx) noexcept;
 	friend uint64_t ticksMs(Context *ctx) noexcept;
@@ -82,6 +82,8 @@ class Context {
 		AssetManager assetManager;
 		int uninterruptedRefreshes = 3;
 		ox::UniquePtr<BaseClipboardObject> clipboard;
+#else
+		bool running = true;
 #endif
 	protected:
 #ifndef OX_BARE_METAL