Add template annotations for Parle\Stack

Parle/Stack.php

@@ -4,6 +4,9 @@ namespace Parle;
 
 use JetBrains\PhpStorm\Immutable;
 
+/**
+ * @template TValue
+ */
 class Stack
 {
     /* Properties */
@@ -20,7 +23,7 @@ class Stack
     public $size = 0;
 
     /**
-     * @var mixed Element on the top of the stack.
+     * @var TValue Element on the top of the stack.
      */
     public $top;
 
@@ -37,7 +40,7 @@ class Stack
      * Push an item into the stack
      *
      * @link https://php.net/manual/en/parle-stack.push.php
-     * @param mixed $item Variable to be pushed.
+     * @param TValue $item Variable to be pushed.
      * @return void
      */
     public function push($item) {}