add phpstan

Author: dannyvankooten

.gitignore

@@ -0,0 +1 @@
+vendor

composer.json

@@ -3,5 +3,16 @@
   "type": "wordpress-plugin",
   "require": {
     "composer/installers": "^2.0"
+  },
+  "require-dev": {
+    "phpstan/phpstan": "^2.1",
+    "szepeviktor/phpstan-wordpress": "^2.0",
+    "phpstan/extension-installer": "^1.4"
+  },
+  "config": {
+    "allow-plugins": {
+      "composer/installers": true,
+      "phpstan/extension-installer": true
+    }
   }
 }