chore: major code cleanup and type safety using phpstan

tests/BusProNet/ApiClientReceiveTest.php

@@ -65,6 +65,9 @@ class ApiClientReceiveTest extends TestCase
         self::assertSame('0000000005Hello', $result);
     }
 
+    /**
+     * @param resource $socket
+     */
     private function invokeReceive($socket): string
     {
         $method = new \ReflectionMethod(ApiClient::class, 'receive');