Consolidate 3 divergent unix-epoch-to-date conversions (avito.py: MSK, documented
#726; avito_houses.py: UTC; avito_imv.py: naive/system-local) plus 3 duplicated
RUS_MONTHS dicts into a single app/services/scrapers/avito_shared.py module.
MSK is the correct canonical representation: Avito displays listing dates
(item-date, publishDate, price-history dates) in Europe/Moscow, and #726 already
established this to avoid off-by-one dates for listings bumped 00:00-03:00 MSK.
startPriceDate/lastPriceDate are always UTC-midnight in the source JSON so MSK
vs UTC never shifts them, but removedDate/publishDate carry real time-of-day and
DO shift for ~12.5% of events (21:00-23:59 UTC/local) once avito_imv.py/
avito_houses.py switch to MSK on the next scrape run.