Raise NotImplementedError in the fan preset guard instead of returning it

[dlxmax]

LGEFanWrapper.async_set_preset builds the exception and returns it:

async def async_set_preset(self, preset: str) -> None:
    """Set fan preset."""
    if self._description.set_fanpreset_fn is None:
        return NotImplementedError()
    await self._description.set_fanpreset_fn(self._api, preset)

so a missing set_fanpreset_fn silently does nothing instead of signalling that the control is unsupported. The caller discards the return value. The two sibling guards in this same file (async_set_percentage, async_set_preset_mode) both raise.

No behaviour change today. None of the four wrapper descriptions defines fanpresets_fn without also defining set_fanpreset_fn, so _attr_preset_modes is only set when the setter exists. preset_modes is therefore None whenever the setter is missing, and LGEFan.async_set_preset_mode already raises before the wrapper is reached. This just keeps the guard correct if that ever stops holding.

Split out of #988 as an unrelated one-line fix.

[dlxmax]

Closing to reopen with a clean single-commit history.