refactor: rename meta to plugin in table header

src/meta_plugin/digest.rs

@@ -173,7 +173,7 @@ impl MetaPlugin for DigestMetaPlugin {
             };
         }
         
-        let mut metadata = Vec::new();
+        let metadata = Vec::new();
 
         // Update outputs based on the selected hash method
         if let Some(hasher) = &mut self.hasher {