logging: clear clippy warnings

This commit contains two changes:

- clear clippy warnigns
- add pkg/logging/Cargo.lock to .gitignore

Signed-off-by: bin liu <bin@hyper.sh>

.gitignore

@@ -3,5 +3,6 @@
 **/*.rej
 **/target
 **/.vscode
+pkg/logging/Cargo.lock
 src/agent/src/version.rs
 src/agent/kata-agent.service

pkg/logging/src/lib.rs

@@ -93,9 +93,7 @@ impl HashSerializer {
         // Take care to only add the first instance of a key. This matters for loggers (but not
         // Records) since a child loggers have parents and the loggers are serialised child first
         // meaning the *newest* fields are serialised first.
-        if !self.fields.contains_key(&key) {
-            self.fields.insert(key, value);
-        }
+        self.fields.entry(key).or_insert(value);
     }
 
     fn remove_field(&mut self, key: &str) {