Make some new functions const.

src/serde/metadata.rs

@@ -278,6 +278,7 @@ impl Engine {
     /// 1) Functions registered into the global namespace
     /// 2) Functions in static modules
     /// 3) Functions in global modules (optional)
+    #[inline(always)]
     pub fn gen_fn_metadata_to_json(&self, include_global: bool) -> serde_json::Result<String> {
         self.gen_fn_metadata_with_ast_to_json(&AST::empty(), include_global)
     }