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 {

src/meta_plugin/hostname.rs

@@ -236,7 +236,7 @@ impl MetaPlugin for HostnameMetaPlugin {
             };
         }
         
-        let mut metadata = Vec::new();
+        let metadata = Vec::new();
         
         // Get the full hostname
         let full_hostname = self.get_hostname();