Improve assignee handling and task assignment logic

- Added `hasAssigneeChanged` method for detecting assignee change
- Updated `onTaskAssigned` logic to trigger only on assignee change

src/Bundle/ChillTaskBundle/Event/AssignTaskEvent.php

@@ -20,7 +20,7 @@ class AssignTaskEvent extends Event
     final public const PERSIST = 'chill_task.assign_task';
     public function __construct(
         private readonly SingleTask $task,
-        private readonly User $assignedUser,
+        private readonly User $initialAssignee,
     ) {}
 
     public function getTask(): SingleTask
@@ -28,8 +28,13 @@ class AssignTaskEvent extends Event
         return $this->task;
     }
 
-    public function getAssignedUser(): User
+    public function getInitialAssignee(): User
     {
-        return $this->assignedUser;
+        return $this->initialAssignee;
+    }
+
+    public function hasAssigneeChanged(): bool
+    {
+        return $this->initialAssignee !== $this->task->getAssignee();
     }
 }