Add vimeo/psalm as dev dependency

Author: devanych

composer.json

@@ -27,7 +27,8 @@
     "require-dev": {
         "httpsoft/http-message": "^1.0",
         "phpunit/phpunit": "^9.3",
-        "squizlabs/php_codesniffer": "^3.5"
+        "squizlabs/php_codesniffer": "^3.5",
+        "vimeo/psalm": "^3.14"
     },
     "autoload": {
         "psr-4": {
@@ -41,10 +42,12 @@
     },
     "scripts": {
         "test": "phpunit --colors=always",
+        "static": "psalm",
         "cs-check": "phpcs",
         "cs-fix": "phpcbf",
         "check": [
             "@cs-check",
+            "@static",
             "@test"
         ]
     }

psalm.xml

@@ -0,0 +1,15 @@
+<?xml version="1.0"?>
+<psalm
+    totallyTyped="true"
+    resolveFromConfigFile="true"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xmlns="https://getpsalm.org/schema/config"
+    xsi:schemaLocation="https://getpsalm.org/schema/config vendor/vimeo/psalm/config.xsd"
+>
+    <projectFiles>
+        <directory name="src" />
+        <ignoreFiles>
+            <directory name="vendor" />
+        </ignoreFiles>
+    </projectFiles>
+</psalm>