feat: Separate in method: _syncLabelForOpenedEmail & add const for LabelKeywordIsNull

lib/features/labels/presentation/mixin/add_label_to_email_mixin.dart

@@ -87,7 +87,7 @@ mixin AddLabelToEmailMixin on EmitStateMixin {
       emitFailure(
         controller: currentController,
         failure: AddALabelToAnEmailFailure(
-          exception: LabelKeywordIsNull(),
+          exception: const LabelKeywordIsNull(),
           labelDisplay: labelDisplay,
         ),
       );
@@ -151,7 +151,7 @@ mixin AddLabelToEmailMixin on EmitStateMixin {
       emitFailure(
         controller: currentController,
         failure: RemoveALabelFromAnEmailFailure(
-          exception: LabelKeywordIsNull(),
+          exception: const LabelKeywordIsNull(),
           labelDisplay: labelDisplay,
         ),
       );

lib/features/mailbox_dashboard/presentation/extensions/labels/handle_logic_label_extension.dart

@@ -49,16 +49,24 @@ extension HandleLogicLabelExtension on MailboxDashBoardController  {
     _refreshLabelSettingEnabled();
 
     if (isEmailOpened) {
-      dispatchEmailUIAction(
-        SyncUpdateLabelForEmailOnMemory(
-          emailId: emailId,
-          labelKeyword: labelKeyword,
-          shouldRemove: shouldRemove,
-        ),
-      );
+      _syncLabelForOpenedEmail(emailId, labelKeyword, shouldRemove);
     }
   }
 
+  void _syncLabelForOpenedEmail(
+    EmailId emailId,
+    KeyWordIdentifier labelKeyword,
+    bool shouldRemove,
+  ) {
+    dispatchEmailUIAction(
+      SyncUpdateLabelForEmailOnMemory(
+        emailId: emailId,
+        labelKeyword: labelKeyword,
+        shouldRemove: shouldRemove,
+      ),
+    );
+  }
+
   void _syncLabelForEmailList(
     EmailId emailId,
     KeyWordIdentifier labelKeyword,