Add DeepSleep log message and improve formatting consistency

- Introduced `DeepSleep` log message for tracking system sleep events.
- Updated MQTT topic to use `/state` instead of `/firmware/state`.
- Improved code formatting for enhanced readability and maintainability.

Software/MainBoard/rust/src/log/mod.rs

@@ -319,6 +319,8 @@ pub enum LogMessage {
     Trace,
     #[strum(serialize = "Parsing error reading message")]
     UnknownMessage,
+    #[strum(serialize = "Going to deep sleep for ${number_a} minutes")]
+    DeepSleep,
 }
 
 #[derive(Serialize)]