Add VM variable storage type

Define a dedicated `vmvar_t` type for values stored in variable pages
and propagate it through interfaces that expose those values. Keep the
type as int for now so this commit does not change runtime behavior.
This separates VM storage from ordinary int buffers and makes a later
conversion to 16-bit storage mechanically checkable.

modules/ShString/ShString.c

@@ -127,7 +127,7 @@ static void SetStringNum16(void) {
 	  p2: 変換された数値を格納する変数
 	*/
 	int st = getCaliValue();
-	int *var = getCaliVariable();
+	vmvar_t *var = getCaliVariable();
 	const char *str = svar_get(st);
 	char _dst[100];
 	char *dst = _dst;
@@ -160,7 +160,7 @@ static void SetStringNum16(void) {
 
 static void SetStringNum32(void) {
 	int p1 = getCaliValue();
-	int *p2 = getCaliVariable();
+	vmvar_t *p2 = getCaliVariable();
 	
 	TRACE_UNIMPLEMENTED("ShString.SetStringNum32: %d,%p:", p1, p2);
 }