Also should it be specific to generators/coroutines and accept PyGenObject* or should it try to handle multiple cases and expose the result for them in uniform way, i.e.
```
if (PyGen_CheckExact(gen) || PyCoro_CheckExact(gen)) {
   // use coroutine/generator specific code that avoids raising exceptions
   *result = ...
   return PYGEN_RETURN;
}
PyObject *ret;
if (arg == Py_None) {
  ret = Py_TYPE(gen)->tp_iternext(gen);
}
else {
  ret = _PyObject_CallMethodIdOneArg(coro, &PyId_send, arg);
}
if (ret != NULL) {
  *result = ret;
  return PYGEN_YIELD;
}
if (_PyGen_FetchStopIterationValue(result) == 0) {
  return PYGEN_RETURN;
}
return PYGEN_ERROR;
```