Fix the reference count stealing problem in clif::callback.

This is a follow up of cl/532595246. When the first parameter of the callback function is not `PyObject*`, and the second parameter of the callback function is `PyObject*`, the newly added function template specialization for `PyObject*` is not executed. See b/282776731#comment6 for details.

TGP only includes unrelated failures: https://fusion2.corp.google.com/presubmit/568959836/OCL:568959836:BASE:569532419:1696009662955:2e10d708/targets.

PiperOrigin-RevId: 576333623

clif/python/stltypes.h

@@ -338,6 +338,11 @@ inline Py_ssize_t ArgIn(PyObject**, Py_ssize_t idx, const py::PostConv&) {
   return idx;
 }
 
+// NOTE: This forward declaration is CRITICAL (see b/282776731#comment6).
+template <typename... T>
+Py_ssize_t ArgIn(PyObject** a, Py_ssize_t idx, const py::PostConv& pc,
+                 PyObject* c1, T&&... c);
+
 template <typename T1, typename... T>
 Py_ssize_t ArgIn(PyObject** a, Py_ssize_t idx, const py::PostConv& pc, T1&& c1,
                  T&&... c) {

clif/testing/python/pyobject_ptr_test.py

@@ -93,22 +93,40 @@ def cb(pvh):
         self.assertEqual(cc(cb_guarded, PyValueHolder(3.0)).value, -123)
       self.assertIn("ValueError: Unknown pvh.value: 3.0", sio.getvalue())
 
-  def test_call_callback_with_pyobject_ptr_int_args(self):
+  def test_call_callback_with_pyobject_ptr_int_args_temporary_arg(self):
     def cb(pvh, num):
       return tst.CppValueHolder(pvh.value * 10 + num)
 
     cc = tst.call_callback_with_pyobject_ptr_int_args
     for _ in range(1000):
       self.assertEqual(cc(cb, PyValueHolder(30)).value, 340)
 
-  def test_call_callback_with_int_pyobject_ptr_args(self):
+  def test_call_callback_with_pyobject_ptr_int_args_named_arg(self):
+    def cb(pvh, num):
+      return tst.CppValueHolder(pvh.value * 10 + num)
+
+    cc = tst.call_callback_with_pyobject_ptr_int_args
+    value_holder = PyValueHolder(30)
+    for _ in range(1000):
+      self.assertEqual(cc(cb, value_holder).value, 340)
+
+  def test_call_callback_with_int_pyobject_ptr_args_temporary_arg(self):
     def cb(num, pvh):
       return tst.CppValueHolder(num * 20 + pvh.value)
 
     cc = tst.call_callback_with_int_pyobject_ptr_args
     for _ in range(1000):
       self.assertEqual(cc(cb, PyValueHolder(60)).value, 1060)
 
+  def test_call_callback_with_int_pyobject_ptr_args_named_arg(self):
+    def cb(num, pvh):
+      return tst.CppValueHolder(num * 20 + pvh.value)
+
+    cc = tst.call_callback_with_int_pyobject_ptr_args
+    value_holder = PyValueHolder(60)
+    for _ in range(1000):
+      self.assertEqual(cc(cb, value_holder).value, 1060)
+
 
 if __name__ == "__main__":
   absltest.main()