Two fixes for the alarm_code diagnostic sensor:
1. _is_included now treats an empty rep ({}) from /device/0 as a stub
meaning the resource exists but hasn't been individually fetched yet.
Previously the field-presence check against {} returned False, leaving
the entity unregistered and showing Unavailable from the entity registry.
2. Replace _last_alarm_code (silently dropped all but the final alarm) with
_active_alarm_codes which joins all codes in the items list. Shows 'none'
when no alarms are active.
Marc Billow
62fc3b44f4