code-reviewer flagged that neither the new parity test nor
test_backfill_wave2.py's 3 cian_price_history tests would catch a
regression if config=RealScraperConfig() were accidentally dropped from
the fetch_detail call in cian_price_history.py (the proxy-footgun fix
from the #2306 migration) — mock_fetch.assert_called_once() doesn't
check kwargs.
Strengthens all 3 tests (saves_changes / skips_no_changes /
handles_fetch_none) to assert isinstance(call_kwargs["config"],
RealScraperConfig). Manually verified the guard actually catches the
regression: temporarily removed config= from cian_price_history.py:110,
confirmed all 3 tests fail, restored the fix, confirmed they pass again.
