Do not instantiate our own CacheItemInterface implementation

As per psr/cache interface:

Calling Libraries MUST NOT instantiate Item objects themselves. They
may only be requested from a Pool object via the getItem() method

src/Decorators/CachingDecorator.php

@@ -7,6 +7,7 @@
 use Chief\Command;
 use Chief\CommandBus;
 use Chief\Decorator;
+use Psr\Cache\CacheItemInterface;
 use Psr\Cache\CacheItemPoolInterface;
 
 class CachingDecorator implements Decorator
@@ -71,15 +72,13 @@ public function execute(Command $command)
      *
      * @param CacheableCommand $command
      * @param mixed $value
-     * @return CacheItem
+     * @return CacheItemInterface
      */
     private function createCacheItem(CacheableCommand $command, $value)
     {
-        return new CacheItem(
-            $this->createCacheKey($command),
-            $value,
-            $this->expiresAfter
-        );
+        return $this->cache->getItem($this->createCacheKey($command))
+            ->set($value)
+            ->expiresAfter($this->expiresAfter);
     }
 
     /**

tests/Decorators/CachingDecoratorTest.php

@@ -52,8 +52,12 @@ public function test_execution_return_value_is_cached_when_command_implements_ca
 
         $notCachedItem = $this->prophesize(CacheItemInterface::class);
         $notCachedItem->isHit()->willReturn(false);
+        $notCachedItem->getKey()->willReturn(md5(serialize(($command))));
         $this->cache->getItem(Argument::any())->willReturn($notCachedItem->reveal());
 
+        $notCachedItem->set(7)->shouldBeCalled()->willReturn($notCachedItem->reveal());
+        $notCachedItem->expiresAfter(3600)->shouldBeCalled()->willReturn($notCachedItem->reveal());
+
         $this->cache->save(Argument::that(function (CacheItemInterface $item) use ($command) {
             return $item->getKey() === md5(serialize($command));
         }))->shouldBeCalled();