3 fixes inside services/estimator.py from 2026-05-24 audit:
* IMV link UPDATE moved inside main tx (finding #4) — closes race where two
concurrent estimates sharing a cache_key could overwrite each other's
estimate_id after the main commit.
* _save_yandex_history_items batched under single try/except (finding #5) —
prior per-item db.rollback() destroyed the parent transaction; next
iteration could run on a rolled-back session.
* Drop redundant CAST inside IS NOT NULL predicates in _fetch_analogs
(finding #9) — CAST(NULL AS T) IS NOT NULL is equivalent to NULL IS NOT NULL
but evaluates per-row. THEN-branch CASTs preserved (typed arithmetic).
test: update test_save_history_items_db_error_continues → batch rollback semantics
