Implement length macro in luaify

crates/luaify/tests/test.rs

@@ -391,3 +391,14 @@ fn variadic() {
         r#"function(a,...)local a,b=a,b,c,...;return func(a,b,c,d,...);end"#
     );
 }
+
+#[test]
+fn length() {
+    assert_eq!(luaify!(len!(a)), r#"#a"#);
+    assert_eq!(
+        luaify!({
+            let (a, b, c) = (len!(a), len!(b), len!(c));
+        }),
+        r#"local a,b,c=#a,#b,#c;"#
+    );
+}