test(anthropic): Stop mocking response iterator

tests/conftest.py

@@ -1013,6 +1013,17 @@ async def inner(values):
     return inner
 
 
+@pytest.fixture
+def server_side_event_chunks():
+    def inner(events):
+        for event in events:
+            payload = event.model_dump()
+            chunk = f"event: {payload['type']}\ndata: {json.dumps(payload)}\n\n"
+            yield chunk.encode("utf-8")
+
+    return inner
+
+
 class MockServerRequestHandler(BaseHTTPRequestHandler):
     def do_GET(self):  # noqa: N802
         # Process an HTTP GET request and return a response.