[PHP 8.4] Fixes for implicit nullability deprecation

Fixes all issues that emit deprecation notices on PHP 8.4 for implicit nullable parameter type declarations.

See:
 - [RFC](https://wiki.php.net/rfc/deprecate-implicitly-nullable-types)
 - [PHP 8.4: Implicitly nullable parameter declarations deprecated](https://php.watch/versions/8.4/implicitly-marking-parameter-type-nullable-deprecated)

src/Manager.php

@@ -17,7 +17,7 @@ class Manager
      * @throws Exception
      * @throws \Exception
      */
-    public function run(Settings $settings = null)
+    public function run(?Settings $settings = null)
     {
         $settings = $settings ?: new Settings;
         $output = $this->output ?: $this->getDefaultOutput($settings);