feat(tradein): extend save_listings INSERT to persist Cian-specific columns (PR #450 follow-up)
Extends base.py save_listings() to persist all 13 Cian-specific columns
added to ScrapedLot in PR #447 and listings DDL in migration 019:
living_area_m2, bedrooms_count, balconies_count, loggias_count,
description_minhash, cadastral_number, building_cadastral_number,
phones, is_homeowner, is_pro_seller, bargain_allowed, sale_type,
metro_stations.
ON CONFLICT DO UPDATE SET extended to refresh all new columns on re-scrape.
Avito/DomRF backward compat: optional fields default None → SQL NULL.
Adds 6 unit tests (test_base_save_listings.py) covering Cian INSERT,
Avito null compat, ON CONFLICT UPDATE SQL text, empty phones/metro → NULL.
702cb2b7d0