add and render HistoryVisibilityContent

lib/models/content/content.dart

@@ -14,6 +14,7 @@ import "package:nexus/models/content/encrypted.dart";
 import "package:nexus/models/content/redaction.dart";
 import "package:nexus/models/content/server_acl.dart";
 import "package:nexus/models/content/topic.dart";
+import "package:nexus/models/content/history_visibility.dart";
 
 class Content {
   final Error? parseError;
@@ -44,6 +45,10 @@ enum EventType {
   encryption("m.room.encryption", EncryptionContent.fromJson),
   membership("m.room.member", MembershipContent.fromJson),
   create("m.room.create", CreateContent.fromJson),
+  historyVisibility(
+    "m.room.history_visibility",
+    HistoryVisibilityContent.fromJson,
+  ),
   canonicalAlias("m.room.canonical_alias", CanonicalAliasContent.fromJson),
   joinRules("m.room.join_rules", JoinRulesContent.fromJson),
   powerLevels("m.room.power_levels", PowerLevelsContent.fromJson),

lib/models/content/history_visibility.dart

@@ -0,0 +1,19 @@
+import "package:freezed_annotation/freezed_annotation.dart";
+import "package:nexus/models/content/content.dart";
+part "history_visibility.freezed.dart";
+part "history_visibility.g.dart";
+
+@freezed
+abstract class HistoryVisibilityContent extends Content
+    with _$HistoryVisibilityContent {
+  HistoryVisibilityContent._();
+  factory HistoryVisibilityContent({
+    required HistoryVisibility historyVisibility,
+  }) = _HistoryVisibilityContent;
+
+  factory HistoryVisibilityContent.fromJson(Map<String, Object?> json) =>
+      _$HistoryVisibilityContentFromJson(json);
+}
+
+@JsonEnum(fieldRename: FieldRename.snake)
+enum HistoryVisibility { invited, joined, shared, worldReadable }