add most models needed for invites

lib/models/invited_room.dart

@@ -0,0 +1,21 @@
+import "package:fast_immutable_collections/fast_immutable_collections.dart";
+import "package:freezed_annotation/freezed_annotation.dart";
+import "package:nexus/models/epoch_date_time_converter.dart";
+import "package:nexus/models/event.dart";
+
+part "invited_room.freezed.dart";
+part "invited_room.g.dart";
+
+@Freezed(toJson: false, fromJson: false)
+@JsonSerializable()
+class const InvitedRoom({
+  required final String roomId,
+  @EpochDateTimeConverter() required final DateTime createdAt,
+  // TODO: This is DBEvent, should be event.Event
+  required final IList<Event> inviteState,
+}) with _$InvitedRoom {
+  Map<String, Object?> toJson() => _$InvitedRoomToJson(this);
+
+  factory InvitedRoom.fromJson(Map<String, Object?> json) =>
+      _$InvitedRoomFromJson(json);
+}