Improve type hints for test client response.context

[adamchainz]

I have made things!

Adding django-stubs to a project with a number of tests that make assertions against the test client's response.context like:

class FolderListViewTest(TestCase):
    def test_search_filter(self, url, category):
        ...
        response = self.client.get("/example"/)
        ...
        assert response.context["page_obj"] == []

This was resulting in errors like:

example/tests/test_views.py:110: error: No overload variant of "__getitem__" of "list" matches argument type "str"  [call-overload]
example/tests/test_views.py:110: note: Possible overload variants:
example/tests/test_views.py:110: note:     def __getitem__(self, SupportsIndex) -> Dict[str, Any]
example/tests/test_views.py:110: note:     def __getitem__(self, slice) -> List[Dict[str, Any]]

context is gathered in store_rendered_templates and attached in Client.request() / AsyncClient.request(), with possible flattening. It’s always a ContextList.

This PR improves the type hints for ContextList to handle all the types it accepts, and updates _MonkeyPatchedWSGIResponse / _MonkeyPatchedASGIResponse. I used these hints with that project and many issues are fixed.

Related issues

n/a