fan: adopt percentage-based speeds, migrate to state-change event helper, and harden command validation

[mode0192]

This PR addresses issues in the SmartIR Fan component:

Fixes state restoration after Home Assistant restart by using the 'percentage' attribute instead of 'speed'. Improves oscillation handling by only sending commands when the state changes. Enhances power sensor integration to set a valid speed instead of None.

These changes ensure the fan's UI state matches its physical state after restarts and improve reliability with external controls. Tested and works in my setup.