add event search

Fixes #77

lib/models/requests/search.dart

@@ -0,0 +1,21 @@
+import "package:fast_immutable_collections/fast_immutable_collections.dart";
+import "package:freezed_annotation/freezed_annotation.dart";
+
+part "search.freezed.dart";
+part "search.g.dart";
+
+@Freezed(toJson: false, fromJson: false)
+@JsonSerializable(includeIfNull: false)
+class const SearchRequest({
+  required final String searchTerm,
+  final IList<String> roomIds = const .empty(),
+  final int limit = 20,
+  final bool sortByTime = true,
+
+  final String? nextBatch,
+}) with _$SearchRequest {
+  Map<String, Object?> toJson() => _$SearchRequestToJson(this);
+
+  factory SearchRequest.fromJson(Map<String, Object?> json) =>
+      _$SearchRequestFromJson(json);
+}