add support for creating rooms

Fixes #81

lib/models/requests/create_room.dart

@@ -0,0 +1,52 @@
+import "package:fast_immutable_collections/fast_immutable_collections.dart";
+import "package:freezed_annotation/freezed_annotation.dart";
+import "package:nexus/models/content/content.dart";
+import "package:nexus/models/content/encryption.dart";
+
+part "create_room.freezed.dart";
+part "create_room.g.dart";
+
+@Freezed(toJson: false, fromJson: false)
+@JsonSerializable(includeIfNull: false)
+class const CreateRoomRequest({
+  final RoomVisibility? visibility,
+  final String? roomAliasName,
+  final String? name,
+  final String? topic,
+  final IList<String> invite = const IList.empty(),
+  @JsonKey(name: "uk.timedout.msc4491.invite_reason")
+  final String? inviteReason,
+  final IList<InitialStateEvent> initialState = const IList.empty(),
+  final RoomPreset? preset,
+  final bool isDirect = false,
+  final IMap<String, dynamic>? creationContent,
+}) with _$CreateRoomRequest {
+  Map<String, Object?> toJson() => _$CreateRoomRequestToJson(this);
+
+  factory CreateRoomRequest.fromJson(Map<String, Object?> json) =>
+      _$CreateRoomRequestFromJson(json);
+}
+
+@Freezed(toJson: false, fromJson: false)
+@JsonSerializable()
+class const InitialStateEvent({
+  required final String type,
+  final String stateKey = "",
+  required final Content content,
+}) with _$InitialStateEvent {
+  static final encryption = InitialStateEvent(
+    type: EventType.encryption.type,
+    content: EncryptionContent(algorithm: "m.megolm.v1.aes-sha2"),
+  );
+
+  Map<String, Object?> toJson() => _$InitialStateEventToJson(this);
+
+  factory InitialStateEvent.fromJson(Map<String, Object?> json) =>
+      _$InitialStateEventFromJson(json);
+}
+
+@JsonEnum(fieldRename: .snake)
+enum RoomVisibility { public, private }
+
+@JsonEnum(fieldRename: .snake)
+enum RoomPreset { privateChat, publicChat, trustedPrivateChat }