Declare callable return type

The subclass may declare a more specific return type. Explicitly annotating it makes psalm aware that FuncService can only ever return callables and thus prevents a MixedFunctionCall error

src/Factories/FuncService.php

@@ -56,6 +56,7 @@ public function __construct(array $dependencies, callable $function)
 
     /**
      * @inheritDoc
+     * @return callable
      */
     public function __invoke(ContainerInterface $c)
     {