bpo-46110: Add a recursion check to avoid stack overflow in the PEG parser (GH-30177)

Co-authored-by: Batuhan Taskaya <isidentical@gmail.com>

Parser/pegen.c

@@ -815,6 +815,7 @@ void *
 _PyPegen_run_parser(Parser *p)
 {
     void *res = _PyPegen_parse(p);
+    assert(p->level == 0);
     if (res == NULL) {
         if (PyErr_Occurred() && !PyErr_ExceptionMatches(PyExc_SyntaxError)) {
             return NULL;