chore: set PHPStan to level 5 with baseline

.phive/phars.xml

 <?xml version="1.0" encoding="UTF-8"?>
 <phive xmlns="https://phar.io/phive">
-  <phar name="phpstan" version="1.11.1" installed="1.11.1" location="./tools/phpstan" copy="false"/>
+  <phar name="phpstan" version="1.11.8" installed="1.11.8" location="./tools/phpstan" copy="false"/>
   <phar name="phpunit" version="^10.5.20" installed="10.5.20" location="./tools/phpunit" copy="false"/>
   <phar name="phpcs" version="^3.10.1" installed="3.10.1" location="./tools/phpcs" copy="false"/>
   <phar name="phpcbf" version="^3.10.1" installed="3.10.1" location="./tools/phpcbf" copy="false"/>

phpstan.dist.neon

@@ -2,7 +2,7 @@ includes:
     - phpstan-baseline.neon
 
 parameters:
-    level: 1
+    level: 5
     paths:
         - src
         - ajax