test: replace _CustomPage helper with SimpleNamespace

Removes boilerplate for the additional_data fallback test without
losing coverage of that code path.

Author: DPGrev

tests/tasks/test_page_iterator.py

@@ -1,4 +1,5 @@
 import os
+from types import SimpleNamespace
 from unittest.mock import AsyncMock, patch, Mock
 
 import pytest
@@ -125,24 +126,16 @@ async def test_delta_link_updated_from_final_page():
     assert page_iterator.delta_link == 'https://graph.microsoft.com/v1.0/delta?token=final'
 
 
-class _CustomPage:  # pylint: disable=too-few-public-methods
-    """A page response whose model does not declare 'odata_delta_link' and
-    instead carries it in the additional data bag, like a Kiota-generated
-    collection response that doesn't model the deltaLink property."""
-
-    def __init__(self, value, odata_next_link=None, additional_data=None):
-        self.value = value
-        self.odata_next_link = odata_next_link
-        self.additional_data = additional_data or {}
-
-
 @pytest.mark.asyncio
 async def test_delta_link_falls_back_to_additional_data():
     """Reproduces the gap where a model without a typed 'odata_delta_link'
-    attribute stores the delta link in additional_data instead."""
+    attribute stores the delta link in additional_data instead, like a
+    Kiota-generated collection response that doesn't model the deltaLink
+    property."""
     first_page = PageResult(odata_next_link='https://graph.microsoft.com/v1.0/next', value=[1, 2])
-    final_page = _CustomPage(
+    final_page = SimpleNamespace(
         value=[3, 4],
+        odata_next_link=None,
         additional_data={'@odata.deltaLink': 'https://graph.microsoft.com/v1.0/delta?token=final'},
     )