feat: add psalm

closes #16

Signed-off-by: Dmitriy Bespalov <[email protected]>

Author: superrosko

composer.json

@@ -28,7 +28,9 @@
     "require-dev": {
         "laminas/laminas-coding-standard": "~2.2.0",
         "laminas/laminas-stdlib": "^2.7.8 || ^3.0.1",
-        "phpunit/phpunit": "^7.5.15"
+        "phpunit/phpunit": "^9.3",
+        "vimeo/psalm": "^4.7",
+        "psalm/plugin-phpunit": "^0.16.0"
     },
     "autoload": {
         "psr-4": {
@@ -47,6 +49,7 @@
         ],
         "cs-check": "phpcs",
         "cs-fix": "phpcbf",
+        "static-analysis": "psalm --shepherd --stats",
         "test": "phpunit --colors=always",
         "test-coverage": "phpunit --colors=always --coverage-clover clover.xml"
     },