Optimize the execution time of the unique method (#39822)

* Optimize the execution time of the unique method

When passing a large array, the unique method is very slow. 
This modification can increase the speed by hundreds of times, 
and it is also suitable for most scenarios.

* Optimize the execution time of the unique method

* Update Collection.php

Co-authored-by: Taylor Otwell <taylor@laravel.com>

src/Illuminate/Collections/Collection.php

@@ -1454,6 +1454,10 @@ public function undot()
      */
     public function unique($key = null, $strict = false)
     {
+        if (is_null($key) && $strict === false) {
+            return new static(array_unique($this->items, SORT_REGULAR));
+        }
+
         $callback = $this->valueRetriever($key);
 
         $exists = [];