[5.x] Simplify collection and cache getComputedCallbacks on Entry i…

…nstances (#9642)

Co-authored-by: Jason Varga <jason@pixelfear.com>

src/Entries/Entry.php

@@ -78,6 +78,7 @@ class Entry implements Arrayable, ArrayAccess, Augmentable, ContainsQueryableVal
     protected $withEvents = true;
     protected $template;
     protected $layout;
+    private $computedCallbackCache;
     private $siteCache;
 
     public function __construct()
@@ -128,6 +129,7 @@ public function collection($collection = null)
             }) : null;
         }
 
+        $this->computedCallbackCache = null;
         $this->collection = $collection instanceof \Statamic\Contracts\Entries\Collection ? $collection->handle() : $collection;
 
         return $this;
@@ -1019,7 +1021,11 @@ public function getCpSearchResultBadge(): string
 
     protected function getComputedCallbacks()
     {
-        return Facades\Collection::getComputedCallbacks($this->collection);
+        if ($this->computedCallbackCache) {
+            return $this->computedCallbackCache;
+        }
+
+        return $this->computedCallbackCache = Facades\Collection::getComputedCallbacks($this->collection);
     }
 
     public function __sleep()
@@ -1029,6 +1035,6 @@ public function __sleep()
             $this->slug = $slug($this);
         }
 
-        return array_keys(get_object_vars($this));
+        return array_keys(Arr::except(get_object_vars($this), ['computedCallbackCache']));
     }
 }