feat:更新代办事项存储功能

lib/models/todo.g.dart

@@ -17,7 +17,7 @@ class TodoAdapter extends TypeAdapter<Todo> {
       for (int i = 0; i < numOfFields; i++) reader.readByte(): reader.read(),
     };
     return Todo(
-      id: fields[0] as int?,
+      id: fields[0] as int,
       title: fields[1] as String,
       content: fields[2] as String,
       isCompleted: fields[3] as bool,