feat(dfu): add firmware file selection and validation

lib/model/firmware_file_selection.dart

@@ -0,0 +1,70 @@
+import 'dart:typed_data';
+
+class DfuV1FirmwareMetadata {
+  const DfuV1FirmwareMetadata({
+    required this.totalLength,
+    required this.crc32,
+    required this.sessionId,
+    required this.flags,
+  });
+
+  final int totalLength;
+  final int crc32;
+  final int sessionId;
+  final int flags;
+}
+
+class DfuV1PreparedFirmware {
+  const DfuV1PreparedFirmware({
+    required this.fileName,
+    required this.fileBytes,
+    required this.metadata,
+    this.filePath,
+  });
+
+  final String fileName;
+  final String? filePath;
+  final Uint8List fileBytes;
+  final DfuV1FirmwareMetadata metadata;
+}
+
+enum FirmwareSelectionFailureReason {
+  canceled,
+  malformedSelection,
+  unsupportedExtension,
+  emptyFile,
+  readFailed,
+}
+
+class FirmwareSelectionFailure {
+  const FirmwareSelectionFailure({
+    required this.reason,
+    required this.message,
+  });
+
+  final FirmwareSelectionFailureReason reason;
+  final String message;
+}
+
+class FirmwareFileSelectionResult {
+  const FirmwareFileSelectionResult._({
+    this.firmware,
+    this.failure,
+  });
+
+  final DfuV1PreparedFirmware? firmware;
+  final FirmwareSelectionFailure? failure;
+
+  bool get isSuccess => firmware != null;
+
+  bool get isCanceled =>
+      failure?.reason == FirmwareSelectionFailureReason.canceled;
+
+  static FirmwareFileSelectionResult success(DfuV1PreparedFirmware firmware) {
+    return FirmwareFileSelectionResult._(firmware: firmware);
+  }
+
+  static FirmwareFileSelectionResult failed(FirmwareSelectionFailure failure) {
+    return FirmwareFileSelectionResult._(failure: failure);
+  }
+}