Add power-canister environmental telemetry

Expose front and rear ESC-board temperature in degrees Celsius and relative humidity in percent. Keep each board optional so unavailable readings are distinguishable from zero.

Co-authored-by: Astra <noreply@openai.com>

Author: sindrehan

protobuf_definitions/message_formats.proto

@@ -359,6 +359,18 @@ message CanisterHumidity {
   float humidity = 3; // Air humidity (%).
 }
 
+// Environmental measurements inside the X7 power canister.
+message PowerCanister {
+  // Temperature and relative humidity measured by an ESC board's SHT40 sensor.
+  message Environment {
+    float temperature = 1; // Temperature (°C).
+    float humidity = 2; // Relative humidity (%).
+  }
+
+  Environment front_esc = 1; // Front ESC board; absent when no recent reading is available.
+  Environment rear_esc = 2; // Rear ESC board; absent when no recent reading is available.
+}
+
 // Essential battery information.
 message Battery {
   float voltage = 1; // Battery voltage (V).

protobuf_definitions/telemetry.proto

@@ -164,6 +164,11 @@ message CanisterBottomHumidityTel {
   CanisterHumidity humidity = 1; // Humidity information.
 }
 
+// Receive environmental measurements from the X7 power canister at 1 Hz.
+message PowerCanisterTel {
+  PowerCanister power_canister = 1; // Front and rear ESC-board temperature and humidity.
+}
+
 // Video storage info.
 message VideoStorageSpaceTel {
   StorageSpace storage_space = 1; // Internal Video storage information.