refactor: move Solar struct to mqtt module

rust/src/mqtt.rs

@@ -27,6 +27,12 @@ pub struct PumpInfo {
     pub min_current_ma: u16,
 }
 
+#[derive(Serialize, Debug, PartialEq)]
+pub struct Solar {
+    pub current_ma: u32,
+    pub voltage_ma: u32,
+}
+
 static MQTT_CONNECTED_EVENT_RECEIVED: AtomicBool = AtomicBool::new(false);
 static MQTT_ROUND_TRIP_RECEIVED: AtomicBool = AtomicBool::new(false);
 pub static MQTT_STAY_ALIVE: AtomicBool = AtomicBool::new(false);