Fix unload KeyError for failed device setup

[geekypilot]

Summary

This fixes an unload crash that can happen when a Tuya device is offline during Home Assistant startup. In that state Home Assistant may leave the config entry in setup_retry, while tuya-local never finishes creating the usual cached device data under hass.data.

Later, when Home Assistant reloads, updates, or shuts down that entry, the integration still runs its unload path. Before this change, that path assumed the cached device entry and all of its internal keys existed, so it could raise a KeyError instead of completing the unload.

This PR makes that cleanup path defensive for setup-failed entries:

• async_unload_entry now tolerates a missing hass.data[DOMAIN][device_id] entry and treats it as already unloaded.
• async_delete_device now tolerates missing or partially initialized cached handles.
• Device cleanup still awaits async_stop() before removing the cached device object, so a stop failure does not silently discard the device reference first.

The intent is to keep normal unload behavior unchanged for devices that completed setup, while preventing failed setup or setup_retry entries from crashing later reload/update/shutdown flows.

Reported traceback

Traceback (most recent call last):
  File "/config/custom_components/tuya_local/__init__.py", line 1001, in async_update_entry
    await async_unload_entry(hass, entry)
  File "/config/custom_components/tuya_local/__init__.py", line 993, in async_unload_entry
    await async_delete_device(hass, config)
  File "/config/custom_components/tuya_local/device.py", line 822, in async_delete_device
    del hass.data[DOMAIN][device_id]["device"]
KeyError: '<device_id>'

Device context

• Device: Venta AH550 humidifier, detected as type venta_ah510_humidifier.
• Setup state: offline during Home Assistant boot, leaving the entry in setup_retry.
• Entry reason: tuya-local device offline.
• Related issues: Request support for VANCOO TGM50-WIFI-EP #3824, Request support for SLS BELL-03 #3174.

Scope notes

This PR is intentionally narrow. It addresses unload cleanup for setup-failed or partially initialized entries, but does not try to redesign broader cache recovery behavior. In particular, it does not add new handling for unrelated cases where platform entities were already forwarded and the device cache is later externally corrupted.

Testing

• uv run pytest tests/test_config_flow.py::test_async_unload_entry_ignores_missing_device_data -q
• uv run pytest tests/test_device.py::test_delete_keeps_device_entry_when_stop_fails -q
• uv run pytest tests/test_device.py tests/test_config_flow.py -q
• uv run pytest
• uv run ruff check .
• uv run ruff check --select I .
• uv run ruff format --check .
• uv run yamllint custom_components/tuya_local/devices