Add room upgrades

Fixes #155

lib/models/capabilities.dart

@@ -1,3 +1,4 @@
+import "package:fast_immutable_collections/fast_immutable_collections.dart";
 import "package:freezed_annotation/freezed_annotation.dart";
 
 part "capabilities.freezed.dart";
@@ -7,6 +8,7 @@ part "capabilities.g.dart";
 @JsonSerializable()
 class const Capabilities({
   @JsonKey(name: "org.matrix.msc4174.webpush") final WebPush? webpush,
+  @JsonKey(name: "m.room_versions") final RoomVersions? roomVersions,
 }) with _$Capabilities {
   Map<String, Object?> toJson() => _$CapabilitiesToJson(this);
 
@@ -23,3 +25,30 @@ class const WebPush({required final bool enabled, final String? vapid})
   factory WebPush.fromJson(Map<String, Object?> json) =>
       _$WebPushFromJson(json);
 }
+
+@Freezed(toJson: false, fromJson: false)
+@JsonSerializable()
+class const RoomVersions({
+  @JsonKey(name: "default") required final String defaultVersion,
+  @JsonKey(fromJson: RoomVersionStability.mapFromJson)
+  required final IMap<String, RoomVersionStability> available,
+}) with _$RoomVersions {
+  Map<String, Object?> toJson() => _$RoomVersionsToJson(this);
+
+  factory RoomVersions.fromJson(Map<String, Object?> json) =>
+      _$RoomVersionsFromJson(json);
+}
+
+enum RoomVersionStability {
+  stable,
+  unstable,
+  unknown;
+
+  static IMap<String, RoomVersionStability> mapFromJson(
+    Map<String, dynamic> json,
+  ) => IMap.fromJson(
+    json,
+    (version) => version as String,
+    (stability) => values.asNameMap()[stability] ?? unknown,
+  );
+}