Add composer scripts

- php-cs-fixer
- phpstan
- unit tests (phpunit)

For now, scripts are running to check only on src/ directory

To run the CI script:
`composer run ci`

composer.json

@@ -92,7 +92,15 @@
         ],
         "post-update-cmd": [
             "@auto-scripts"
-        ]
+        ],
+        "ci": [
+            "@php-cs-fixer",
+            "@phpstan",
+            "@unit-tests"
+        ],
+        "php-cs-fixer": "tools/php-cs-fixer/vendor/bin/php-cs-fixer fix src/",
+        "phpstan": "vendor/bin/phpstan analyse src/",
+        "unit-tests": "php ./vendor/bin/phpunit"
     },
     "conflict": {
         "symfony/symfony": "*"