Fix isspace implementation

rt/include/python/builtins/str.hpp

@@ -49,7 +49,7 @@ public:
           })
 
   METHOD(bool, isspace, (Self self), {
-       return std::all_of(self.begin(), self.end(), isspace);
+       return self.find_first_not_of(' ') == std::string::npos;
                                      })
 
   METHOD(auto, py_contains, (Self self, const std::string &x), {