Do not cache ItemStacks for every item

this is very memory inefficient, and only provides a performance advantage in cold code anyway.

src/network/mcpe/ItemStackInfo.php

@@ -23,19 +23,14 @@ declare(strict_types=1);
 
 namespace pocketmine\network\mcpe;
 
-use pocketmine\network\mcpe\protocol\types\inventory\ItemStack;
-
 final class ItemStackInfo{
 
 	public function __construct(
 		private ?int $requestId,
-		private int $stackId,
-		private ItemStack $itemStack
+		private int $stackId
 	){}
 
 	public function getRequestId() : ?int{ return $this->requestId; }
 
 	public function getStackId() : int{ return $this->stackId; }
-
-	public function getItemStack() : ItemStack{ return $this->itemStack; }
 }