Investigated with a real curl_cffi capture (HTTP 200, 46 cards): the Avito
SERP lazy-renders — data-marker="item-date" appears only on the top
above-the-fold cards (~10/46), so ~79% of cards have no date in the raw HTML
curl_cffi receives. The marker wasn't renamed; the field is just absent.
But every listing carries sortTimeStamp (epoch-ms) in the embedded per-item
JSON (56 occurrences/page) — the line-266 'state empty' note was stale. Map
item_id (= DOM data-item-id) -> sortTimeStamp -> date as the primary source,
keep the DOM item-date + _parse_relative_date as fallback for the top cards.
Verified on the real capture: 42/46 = 91% coverage (was ~21% DOM-only),
clearing the >80% DoD bar. Adds a distilled real-structure fixture
(avito_serp_sample.html) + unit test covering both the JSON (lazy card) and
DOM (top card) paths.
Refs #726
