topshift-trend: a transient failure no longer wipes out what was already delivered

A scheduled notify pass in topshift-trend can now fail halfway without repeating itself: per-chat deliveries are recorded as they succeed, so the next run skips the links a chat already received and retries only the ones that never went out, and the global cooldown baseline advances only after a clean pass (0ce1688, PR #9). Before this, one transient Telegram error in the middle of a batch could resend everything that had already arrived. A ruff UP035 fix — Mapping imported from collections.abc — rode along.