streamline tank state mqtt information structure

rust/src/tank.rs

@@ -113,6 +113,14 @@ impl TankState {
         }
     }
 
+    pub fn got_error(&self, config: &TankConfig) -> Option<TankError> {
+        match self {
+            TankState::TankSensorPresent(raw_value_mv) => raw_voltage_to_tank_fill_percent(*raw_value_mv, config).err(),
+            TankState::TankSensorError(err) => Some(err.clone()),
+            TankState::TankSensorDisabled => Some(TankError::SensorDisabled),
+        }
+    }
+
     pub fn as_mqtt_info(&self, config: &TankConfig, water_temp: Result<f32, anyhow::Error>) -> TankInfo {
         let mut tank_err: Option<TankError> = None;
         let left_ml = match self.left_ml(config) {