Use more "First class callable syntax" + Normalize set_error_handler/set_exception_handler calls

Author: lyrixx

Filesystem.php

@@ -749,7 +749,7 @@ private static function box(string $func, mixed ...$args): mixed
         self::assertFunctionExists($func);
 
         self::$lastError = null;
-        set_error_handler(__CLASS__.'::handleError');
+        set_error_handler(self::handleError(...));
         try {
             return $func(...$args);
         } finally {