sensor.py: native_unit_of_measurement not set when coordinator data is None at startup

[dominikprucha]

Version: 2.2.0
HA Version: (2026.5)

Problem:
After HA restart, all observation sensors (temperature, dewpoint, pressure, wind speed, etc.)
lose their unit_of_measurement. HA then reports "units changed" errors in Repairs for all affected entities.

Root cause:
In sensor.py __init__, the unit is only set when self._sensor_data is not None:

if self._sensor_data is not None:
    unit = self.entity_description.unit_fn(...)
    if unit is not None:
        self._attr_native_unit_of_measurement = unit

At startup, the coordinator has not yet loaded data, so _sensor_data is always None
and the unit is never set. After data loads via _handle_coordinator_update,
the value updates but the unit is still missing.

Fix:
Remove the outer if self._sensor_data is not None guard — unit_fn does not depend
on sensor data at all. Text sensors are already handled by the inner if unit is not None check.

unit = self.entity_description.unit_fn(
    self.coordinator.hass.config.units is METRIC_SYSTEM
)
if unit is not None:
    self._attr_native_unit_of_measurement = unit

[cytech]

this is fixed in v2.3.0