Static analysis improvements (#1475)

* Static analysis improvements

* Fix review issues

src/Monolog/Handler/ProcessableHandlerInterface.php

@@ -23,6 +23,8 @@ interface ProcessableHandlerInterface
     /**
      * Adds a processor in the stack.
      *
+     * @psalm-param ProcessorInterface|callable(array): array $callback
+     *
      * @param  ProcessorInterface|callable $callback
      * @return HandlerInterface            self
      */
@@ -31,6 +33,8 @@ interface ProcessableHandlerInterface
     /**
      * Removes the processor on top of the stack and returns it.
      *
+     * @psalm-return callable(array): array
+     *
      * @throws \LogicException In case the processor stack is empty
      * @return callable
      */