[php-src] PR #25231: Fix GH-11821: Allow graceful exit during class fetch without uncaught error

Pull Request: https://github.com/php/php-src/pull/25231 Author: prateekbhujel Closes GH-11821. ### Description When an autoloader or error handler terminates via exit() during a class fetch where exceptions cannot be thrown (such as trait resolution), report_class_fetch_error() previously passed the in-flight UnwindExit to zend_exception_uncaught_error(). Because UnwindExit is an internal unwinding sentinel that does not implement string conversion, zend_exception_uncaught_error() failed when calling zval_get_string(), emitting: ``` Warning: Uncaught Error: Object of class UnwindExit could not be converted to string Fatal error: During class fetch: Uncaught in ... ``` This forced exit status 255 and bypassed object destructors. ### Fix In report_class_fetch_error(), check if EG(exception) is an UnwindExit or GracefulExit and return early. This allows the class declaration opcode (ZEND_DECLARE_CLASS) to proceed to ZEND_VM_NEXT_OPCODE_CHECK_EXCEPTION(), letting the Zend VM opcode loop gracefully unwind the stack, invoke active destructors, and exit cleanly with the requested status.