refactor: BatteryInfo structure (consistent layout)

- use tagged enum serialization for BatteryError
- flatten BatteryInfo telemetry with consistent field names and typed error

Software/MainBoard/rust/src/hal/battery.rs

@@ -1,5 +1,6 @@
 use crate::fat_error::{FatError, FatResult};
 use crate::hal::Box;
+use alloc::string::String;
 use async_trait::async_trait;
 use embassy_embedded_hal::shared_bus::blocking::i2c::I2cDevice;
 use embassy_sync::blocking_mutex::raw::CriticalSectionRawMutex;
@@ -18,15 +19,23 @@ pub trait BatteryInteraction {
     async fn reset(&mut self) -> FatResult<()>;
 }
 
-#[derive(Debug, Serialize, Copy, Clone)]
+#[derive(Debug, Serialize, Clone)]
 pub struct BatteryInfo {
-    pub voltage_milli_volt: u32,
-    pub average_current_milli_ampere: i32,
-    pub design_milli_ampere_hour: u32,
-    pub remaining_milli_ampere_hour: u32,
-    pub state_of_charge: u8,
-    pub state_of_health: u32,
-    pub temperature: i32,
+    pub voltage_mv: Option<u32>,
+    pub avg_current_ma: Option<i32>,
+    pub design_mah: Option<u32>,
+    pub remaining_mah: Option<u32>,
+    pub soc_pct: Option<f32>,
+    pub soh_pct: Option<f32>,
+    pub temperature_c: Option<i32>,
+    pub error: Option<BatteryError>,
+}
+
+#[derive(Debug, Serialize, Clone)]
+#[serde(tag = "kind")]
+pub enum BatteryError {
+    NoBatteryMonitor,
+    CommunicationError { message: String },
 }
 
 #[derive(Debug, Serialize)]
@@ -71,17 +80,18 @@ impl BatteryInteraction for WCHI2CSlave<'_> {
         let config = Config::read_from_i2c(&mut self.i2c)?;
 
         let state_of_charge =
-            (state.remaining_capacity_mah * 100 / state.lifetime_capacity_mah) as u8;
-        let state_of_health = state.lifetime_capacity_mah / config.capacity_mah * 100;
+            state.remaining_capacity_mah as f32 * 100. / state.lifetime_capacity_mah as f32;
+        let state_of_health = state.lifetime_capacity_mah as f32 / config.capacity_mah as f32 * 100.;
 
         Ok(BatteryState::Info(BatteryInfo {
-            voltage_milli_volt: state.current_mv,
-            average_current_milli_ampere: 1337,
-            design_milli_ampere_hour: config.capacity_mah,
-            remaining_milli_ampere_hour: state.remaining_capacity_mah,
-            state_of_charge,
-            state_of_health,
-            temperature: state.temperature_celcius,
+            voltage_mv: Some(state.current_mv),
+            avg_current_ma: Some(1337),
+            design_mah: Some(config.capacity_mah),
+            remaining_mah: Some(state.remaining_capacity_mah),
+            soc_pct: Some(state_of_charge),
+            soh_pct: Some(state_of_health),
+            temperature_c: Some(state.temperature_celcius),
+            error: None
         }))
     }