Add stab tag for metamethods

crates/luaffi/src/internal.rs

@@ -9,12 +9,12 @@ use std::{
 #[allow(non_camel_case_types)]
 pub mod stub_types {
     pub struct any;
-    pub type nil = ();
+    pub struct nil;
     pub type boolean = bool;
-    pub type lightuserdata = *mut ();
-    pub type number = f64;
-    pub type integer = i64;
-    pub type string = &'static str;
+    pub struct lightuserdata;
+    pub struct number;
+    pub struct integer;
+    pub type string = String;
     pub struct table;
     pub struct function;
     pub struct userdata;