created alarm models

lib/model/time_alarm.dart

@@ -0,0 +1,21 @@
+import 'alarm.dart';
+
+class TimeAlarm implements Alarm {
+  @override
+  final String id;
+
+  final DateTime triggerAt;
+
+  const TimeAlarm({required this.id, required this.triggerAt});
+
+  factory TimeAlarm.fromJson(Map<String, dynamic> json) {
+    return TimeAlarm(
+      id: json['id'] as String,
+      triggerAt: DateTime.parse(json['triggerAt'] as String),
+    );
+  }
+
+  Map<String, dynamic> toJson() {
+    return {'id': id, 'triggerAt': triggerAt.toIso8601String()};
+  }
+}