fix(sensor): restore delta semantics for latest_events + fire HA event on new earthquakes (v1.2.6/v1.2.7)

[Copilot]

v1.2.5 introduced a conceptual error: latest_events became a cumulative list that grew on every poll, always exposing all historical events. The correct behaviour is that latest_events is a delta — only events new since the last cycle — so automations trigger exclusively on genuinely new earthquakes.

Behavioral contract (v1.2.6+)

Scenario	latest_events	Sensor state changes	Automation fires
First run / HA restart	All feed events matching filters	✅	✅
Re-poll, no new events	[]	❌	❌
New earthquake detected	New event(s) only	✅	✅

Changes

sensor.py — delta tracking (_seen_ids)

• Replaced the cumulative _latest_events.extend() accumulator with an internal _seen_ids: set[str]. Each cycle, only events absent from _seen_ids are emitted as latest_events; _seen_ids is then updated.
• native_value (TIMESTAMP state) is updated only when new events arrive, so trigger: state fires only on genuine new earthquakes.
• Removed the now-unreachable MAX_EVENTS = 50 constant.

# Before (v1.2.5) — cumulative, never empty after first run
existing_ids = {e["id"] for e in self._latest_events}
self._latest_events.extend([e for e in new_events if e["id"] not in existing_ids])
self._latest_events = sorted(self._latest_events, ...)[:MAX_EVENTS]

# After (v1.2.6) — delta only, backed by a seen-IDs set
filtered_events = [e for e in new_events if e["id"] not in self._seen_ids]
self._seen_ids.update(e["id"] for e in filtered_events)
self._latest_events = sorted(filtered_events, key=parse_event_time, reverse=True)

sensor.py + const.py — HA event bus notification (v1.2.7)

• Added EVENT_NEW_QUAKES = "usgs_earthquakes_feed_new_events" to const.py.
• Sensor fires this event on the HA bus whenever latest_events is non-empty, enabling event-based automations without relying on sensor state polling:

trigger:
  - platform: event
    event_type: usgs_earthquakes_feed_new_events
# event.data: { entry_id, count, events[] }

README

• Replaced stale events / "last 50 events" references with accurate latest_events delta semantics.
• Added dedicated 📣 Event section documenting the new event, its payload, and an example automation.
• Updated 📓 Notes to describe first-run vs. re-poll vs. new-event behaviour.

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