chore: raise phpstan level

Author: Ninerian

phpstan.neon.dist

@@ -1,5 +1,5 @@
 parameters:
-    level: 2
+    level: 3
     paths:
         - ./src
         - ./test

src/AbstractToken.php

@@ -64,7 +64,11 @@ public function __construct(string $appSecret, protected string $tokenData, Sign
     protected function parseToken(): void
     {
         // parse text
-        $this->token = $this->config->parser()->parse($this->tokenData);
+        $token = $this->config->parser()->parse($this->tokenData);
+        if (!$token instanceof Plain) {
+            throw new \RuntimeException('Parsed token is not a Plain token');
+        }
+        $this->token = $token;
     }
 
     /**