Expose LG nature fan speed as auto

[togume]

Summary

Expose LG AC NATURE fan speed as Home Assistant auto instead of diffuse.

Why

Automatic fan speed is unavailable on Apple Home. Some LG mini split models report their automatic fan behavior as NATURE, which currently becomes diffuse in Home Assistant. Since this is the device-managed fan mode, exposing it as standard FAN_AUTO lets Home Assistant and HomeKit Bridge represent it as automatic fan control.

When setting fan_mode: auto, this keeps the existing LG AUTO fallback, but prefers NATURE when the device supports it.

Tests

• pytest tests/test_climate.py
• pytest
• black --line-length 88 --diff --check custom_components/smartthinq_sensors/climate.py tests/test_climate.py
• isort --diff --check custom_components/smartthinq_sensors/climate.py tests/test_climate.py
• flake8 --extend-ignore=E704 custom_components/smartthinq_sensors/climate.py tests/test_climate.py

[togume]

@ollo69 hi hi! WDYT about this change? I've been testing it with a direct patch for over a month and it's been great to have "auto" cooling mode exposed to Apple Home.