New feat

- SFTP download
- open downloaded files in other apps

lib/data/model/sftp/download_status.dart

@@ -0,0 +1,55 @@
+import 'package:toolbox/data/model/sftp/download_worker.dart';
+
+class SftpDownloadStatus {
+  final int id;
+  final DownloadItem item;
+  final void Function() notifyListeners;
+  late SftpDownloadWorker worker;
+
+  String get fileName => item.localPath.split('/').last;
+
+  // status of the download
+  double? progress;
+  SftpWorkerStatus? status;
+  int? size;
+  Exception? error;
+  Duration? spentTime;
+
+  SftpDownloadStatus(this.item, this.notifyListeners, {String? key})
+      : id = DateTime.now().microsecondsSinceEpoch {
+    worker =
+        SftpDownloadWorker(onNotify: onNotify, item: item, privateKey: key);
+    worker.init();
+  }
+
+  @override
+  bool operator ==(Object other) =>
+      other is SftpDownloadStatus && id == other.id;
+
+  @override
+  int get hashCode => id ^ super.hashCode;
+
+  void onNotify(dynamic event) {
+    switch (event.runtimeType) {
+      case SftpWorkerStatus:
+        status = event;
+        break;
+      case double:
+        progress = event;
+        break;
+      case int:
+        size = event;
+        break;
+      case Exception:
+        error = event;
+        break;
+      case Duration:
+        spentTime = event;
+        break;
+      default:
+    }
+    notifyListeners();
+  }
+}
+
+enum SftpWorkerStatus { preparing, sshConnectted, downloading, finished }