Add phpstan level 0 (#1022)

* Remove unused arguments

* Fix return types

* Removed unused parameter and argument

* Add phpstan job

* merge files

* Delete phpstan-baseline.neon

* Delete static-analysis.yml

* merge workflows

* Update composer.json

* format yaml

* install composer reps

* fix yaml

Co-authored-by: Till Krüss <tillkruss@users.noreply.github.com>

src/Cluster/StrategyInterface.php

@@ -29,7 +29,7 @@ interface StrategyInterface
      *
      * @param CommandInterface $command Command instance.
      *
-     * @return int
+     * @return int|null
      */
     public function getSlot(CommandInterface $command);
 
@@ -39,7 +39,7 @@ interface StrategyInterface
      *
      * @param string $key Key string.
      *
-     * @return int
+     * @return int|null
      */
     public function getSlotByKey($key);