fix: update macros

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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: mikkihugo

src/macros.rs

@@ -66,7 +66,7 @@ macro_rules! implement_metric_trait {
 macro_rules! mk_lang {
     ( $( ($camel:ident, $name:ident, $display: expr, $description:expr) ),* ) => {
         /// The list of supported languages.
-        #[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
+        #[derive(Clone, Copy, Debug, PartialEq, Eq, Hash, serde::Serialize, serde::Deserialize)]
         pub enum LANG {
             $(
                 #[doc = $description]