[FL-1994] Add Saved Struct (#804)

Co-authored-by: あく <alleteam@gmail.com>

lib/toolbox/saved_struct.h

@@ -0,0 +1,18 @@
+#pragma once
+
+#include <stdint.h>
+#include <stdbool.h>
+#include <stddef.h>
+
+bool saved_struct_load(const char* path,
+                       void* data,
+                       size_t size,
+                       uint8_t magic,
+                       uint8_t version);
+
+bool saved_struct_save(const char* path,
+                       void* data,
+                       size_t size,
+                       uint8_t magic,
+                       uint8_t version);
+