Show space hierarchies

Fixes #83

lib/models/requests/get_space_hierarchy.dart

@@ -0,0 +1,19 @@
+import "package:freezed_annotation/freezed_annotation.dart";
+
+part "get_space_hierarchy.freezed.dart";
+part "get_space_hierarchy.g.dart";
+
+@Freezed(toJson: false, fromJson: false)
+@JsonSerializable(includeIfNull: false)
+class const GetSpaceHierarchyRequest({
+  required final String roomId,
+  final String? from,
+  final int limit = 50,
+  final int? maxDepth,
+  final bool? suggestedOnly,
+}) with _$GetSpaceHierarchyRequest {
+  Map<String, Object?> toJson() => _$GetSpaceHierarchyRequestToJson(this);
+
+  factory GetSpaceHierarchyRequest.fromJson(Map<String, Object?> json) =>
+      _$GetSpaceHierarchyRequestFromJson(json);
+}

lib/models/space_hierarchy.dart

@@ -0,0 +1,45 @@
+import "package:fast_immutable_collections/fast_immutable_collections.dart";
+import "package:freezed_annotation/freezed_annotation.dart";
+import "package:nexus/models/room_summary.dart";
+
+part "space_hierarchy.freezed.dart";
+part "space_hierarchy.g.dart";
+
+@Freezed(toJson: false, fromJson: false)
+@JsonSerializable(createToJson: false)
+class const SpaceHierarchy({
+  final IList<SpaceHierarchyRoom> rooms = const .empty(),
+  final String? nextBatch,
+}) with _$SpaceHierarchy {
+  factory SpaceHierarchy.fromJson(Map<String, Object?> json) =>
+      _$SpaceHierarchyFromJson(json);
+}
+
+@Freezed(toJson: false, fromJson: false)
+@JsonSerializable(createToJson: false)
+class const SpaceHierarchyRoom({
+  @JsonKey(readValue: SpaceHierarchyRoom.readEntry)
+  required final RoomSummary summary,
+  @JsonKey(name: "children_state")
+  final IList<SpaceHierarchyChild> children = const .empty(),
+}) with _$SpaceHierarchyRoom {
+  static Object? readEntry(Map json, String _) => json;
+
+  factory SpaceHierarchyRoom.fromJson(Map<String, Object?> json) =>
+      _$SpaceHierarchyRoomFromJson(json);
+}
+
+@Freezed(toJson: false, fromJson: false)
+@JsonSerializable(createToJson: false)
+class const SpaceHierarchyChild({
+  @JsonKey(name: "state_key") required final String roomId,
+  @JsonKey(readValue: SpaceHierarchyChild.readContent)
+  final IList<String> via = const .empty(),
+  @JsonKey(readValue: SpaceHierarchyChild.readContent)
+  final bool suggested = false,
+}) with _$SpaceHierarchyChild {
+  static Object? readContent(Map json, String key) => json["content"]?[key];
+
+  factory SpaceHierarchyChild.fromJson(Map<String, Object?> json) =>
+      _$SpaceHierarchyChildFromJson(json);
+}