add phpstan

Author: ArrayIterator

composer.json

@@ -17,7 +17,8 @@
         "psr/cache": "^3",
         "squizlabs/php_codesniffer": "3.7.2",
         "slevomat/coding-standard": "^8.14",
-        "phpunit/phpunit": "^10.4"
+        "phpunit/phpunit": "^10.4",
+        "phpstan/phpstan": "^1.10"
     },
     "config": {
         "optimize-autoloader": true,

phpstan.neon

@@ -0,0 +1,13 @@
+parameters:
+  level: 8
+  checkGenericClassInNonGenericObjectType: false
+  paths:
+    - src
+    - tests
+  fileExtensions:
+    - php
+#  ignoreErrors:
+#    -
+#      message: '#^Method.+::[^\(]+\(\) has no return type#'
+#      paths:
+#        - src/Interfaces/*