factory: reduce enum size

src/entt/meta/factory.hpp

@@ -32,7 +32,7 @@ namespace internal {
 class basic_meta_factory {
     using invoke_type = stl::remove_pointer_t<decltype(meta_func_node::invoke)>;
 
-    enum class mode {
+    enum class mode : std::uint8_t {
         type,
         data,
         func