feat: add shifter trainer scan service

lib/service/shifter_service.dart

@@ -62,6 +62,42 @@ class ShifterService {
     }
   }
 
+  Future<Result<void>> writeConnectToTrainerAddress(
+    TrainerAddress trainerAddress,
+  ) async {
+    try {
+      final payload = encodeTrainerAddress(trainerAddress);
+      return _requireBluetooth.writeCharacteristic(
+        buttonDeviceId,
+        universalShifterControlServiceUuid,
+        universalShifterConnectToAddrCharacteristicUuid,
+        payload,
+      );
+    } on FormatException catch (e) {
+      return bail('Could not encode trainer address: $e');
+    } catch (e) {
+      return bail('Failed writing trainer address: $e');
+    }
+  }
+
+  Stream<TrainerScanEvent> subscribeToTrainerScanResults() {
+    return _requireBluetooth
+        .subscribeToCharacteristic(
+          buttonDeviceId,
+          universalShifterControlServiceUuid,
+          universalShifterScanResultCharacteristicUuid,
+        )
+        .map(TrainerScanEvent.fromBytes);
+  }
+
+  Future<Result<void>> startTrainerScan() {
+    return writeCommand(UniversalShifterCommand.startScan);
+  }
+
+  Future<Result<void>> stopTrainerScan() {
+    return writeCommand(UniversalShifterCommand.stopScan);
+  }
+
   Future<Result<void>> writeCommand(UniversalShifterCommand command) {
     return _requireBluetooth.writeCharacteristic(
       buttonDeviceId,
@@ -79,6 +115,16 @@ class ShifterService {
     return writeCommand(UniversalShifterCommand.connectToDevice);
   }
 
+  Future<Result<void>> connectButtonToTrainer(
+    TrainerAddress trainerAddress,
+  ) async {
+    final addrRes = await writeConnectToTrainerAddress(trainerAddress);
+    if (addrRes.isErr()) {
+      return addrRes;
+    }
+    return writeCommand(UniversalShifterCommand.connectToDevice);
+  }
+
   Future<Result<GearRatiosData>> readGearRatios() async {
     final readRes = await _requireBluetooth.readCharacteristic(
       buttonDeviceId,