Add regression tests pinning the iterator-protocol contract

Review follow-ups on #235: pin that next(name) on the instance raises
TypeError (the documented behavior change — without this, re-adding a
__next__ would pass the existing tests while contradicting the release
log), and that iterating an all-empty name yields nothing now that
__iter__ and __len__ are independent code paths.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: derek73

tests/test_python_api.py

@@ -69,6 +69,19 @@ def test_len_during_iteration(self) -> None:
         self.assertEqual(len(hn), 2)
         self.assertEqual(next(it), "Doe")
 
+    def test_instance_is_not_its_own_iterator(self) -> None:
+        # iterator state must never live on the instance; see release log
+        # for the next(name) -> next(iter(name)) migration
+        hn = HumanName("John Doe")
+        with pytest.raises(TypeError):
+            next(hn)  # type: ignore[call-overload]
+
+    def test_iterating_empty_name_yields_nothing(self) -> None:
+        collected = []
+        for part in HumanName(""):
+            collected.append(part)
+        self.assertEqual(collected, [])
+
     @pytest.mark.skipif(not dill, reason="requires python-dill module to test pickling")
     def test_config_pickle(self) -> None:
         constants = Constants()