use oss-nvjpg for loading jpeg images (homebrew, games and themezer).

slightly faster loading on avg compared to stbi.

sphaira/include/app.hpp

@@ -10,6 +10,7 @@
 #include "fs.hpp"
 #include "log.hpp"
 
+#include <nvjpg.hpp>
 #include <switch.h>
 #include <vector>
 #include <string>
@@ -272,6 +273,8 @@ public:
 
     PLSR_PlayerSoundId m_sound_ids[SoundEffect_MAX]{};
 
+    nj::Decoder m_decoder;
+
 private: // from nanovg decko3d example by adubbz
     static constexpr unsigned NumFramebuffers = 2;
     static constexpr unsigned StaticCmdSize = 0x1000;