fix: add late-arriving thermostats and automations on update

[bluetoothbot]

What

Make _update_devices and _update_automations add-only: a thermostat or automation that first appears on a later fetch is now appended instead of dropped.

Why

Both methods built the entity list once (when it was None) and afterwards only patched entities whose id was already known. Some systems under-report devices on the initial poll, so an entity can be absent at construction and only surface on a subsequent update — and it was being silently ignored forever. This is the same class of bug as #149 (UX360 zones reported after initial discovery), just one level up: whole thermostats and automations rather than zones within a thermostat.

How

• Unified the first-fetch and later-fetch paths: compute the set of already-tracked ids, then append any id present in the new JSON but not yet tracked.
• Preserved the existing zone-skip guard for thermostats with no zones (e.g. xl624).
• Kept existing entity objects intact so consumers holding references (e.g. Home Assistant) keep working. The library never removes thermostats/automations, so add-only is the safe convention — matching the late-zone fix.

Testing

• New regression test_late_thermostat_and_automation_are_added: under-reports one thermostat + one automation on the first update, confirms both are absent, then re-feeds the full payload and asserts both are added while the pre-existing objects are reused (identity check). Fails against the prior code, passes after.
• Full suite: 58 passed, 1 skipped. ruff and mypy nexia/home.py clean.

---

Quality Report

Changes: 2 files changed, 96 insertions(+), 24 deletions(-)

Code scan: clean

Tests: passed (58 passed)

Branch hygiene: clean

Generated by Kōan

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!