The Cian Valuation enrichment was the only ungated external call in
estimate_quality() — its internal curl timeout (~25s) blocks the whole
/estimate request on every cache-miss, intermittently pushing latency
past the gateway/patience window (perceived as 'сервис не считает').
Wrap it in _with_budget() (mirrors the existing Yandex-valuation guard):
on timeout it degrades to None — the same graceful path as a network
error — instead of stalling. New setting estimate_cian_valuation_timeout_s
(default 8.0s, env ESTIMATE_CIAN_VALUATION_TIMEOUT_S).
