Fix PHP 8.1 deprecations (#2452)

* Fix PHP 8.1 deprecations

* Fix CS

* Fix CS using PHP 8.0

Author: jmsche

src/PhpSpreadsheet/Collection/Memory.php

@@ -2,6 +2,7 @@
 
 namespace PhpOffice\PhpSpreadsheet\Collection;
 
+use DateInterval;
 use Psr\SimpleCache\CacheInterface;
 
 /**
@@ -14,20 +15,33 @@ class Memory implements CacheInterface
 {
     private $cache = [];
 
+    /**
+     * @return bool
+     */
     public function clear()
     {
         $this->cache = [];
 
         return true;
     }
 
+    /**
+     * @param string $key
+     *
+     * @return bool
+     */
     public function delete($key)
     {
         unset($this->cache[$key]);
 
         return true;
     }
 
+    /**
+     * @param iterable $keys
+     *
+     * @return bool
+     */
     public function deleteMultiple($keys)
     {
         foreach ($keys as $key) {
@@ -37,6 +51,12 @@ public function deleteMultiple($keys)
         return true;
     }
 
+    /**
+     * @param string $key
+     * @param mixed  $default
+     *
+     * @return mixed
+     */
     public function get($key, $default = null)
     {
         if ($this->has($key)) {
@@ -46,6 +66,12 @@ public function get($key, $default = null)
         return $default;
     }
 
+    /**
+     * @param iterable $keys
+     * @param mixed    $default
+     *
+     * @return iterable
+     */
     public function getMultiple($keys, $default = null)
     {
         $results = [];
@@ -56,18 +82,36 @@ public function getMultiple($keys, $default = null)
         return $results;
     }
 
+    /**
+     * @param string $key
+     *
+     * @return bool
+     */
     public function has($key)
     {
         return array_key_exists($key, $this->cache);
     }
 
+    /**
+     * @param string                 $key
+     * @param mixed                  $value
+     * @param null|DateInterval|int $ttl
+     *
+     * @return bool
+     */
     public function set($key, $value, $ttl = null)
     {
         $this->cache[$key] = $value;
 
         return true;
     }
 
+    /**
+     * @param iterable               $values
+     * @param null|DateInterval|int $ttl
+     *
+     * @return bool
+     */
     public function setMultiple($values, $ttl = null)
     {
         foreach ($values as $key => $value) {