PAD: Intelligently skip saving memcard state for runahead

src/core/memory_card.h

@@ -18,6 +18,8 @@ public:
   MemoryCard();
   ~MemoryCard();
 
+  static constexpr u32 STATE_SIZE = 1 + 1 + 2 + 1 + 1 + 1 + MemoryCardImage::DATA_SIZE + 1;
+
   static std::string SanitizeGameTitleForFileName(const std::string_view& name);
 
   static std::unique_ptr<MemoryCard> Create();