add support for jumping to out-of-context events (#95)

Fixes #84.

Reviewed-on: #95

lib/models/requests/get_event_context.dart

@@ -0,0 +1,17 @@
+import "package:freezed_annotation/freezed_annotation.dart";
+
+part "get_event_context.freezed.dart";
+part "get_event_context.g.dart";
+
+@Freezed(toJson: false, fromJson: false)
+@JsonSerializable()
+class const GetEventContextRequest({
+  required final String roomId,
+  required final String eventId,
+  final int limit = 20,
+}) with _$GetEventContextRequest {
+  Map<String, Object?> toJson() => _$GetEventContextRequestToJson(this);
+
+  factory GetEventContextRequest.fromJson(Map<String, Object?> json) =>
+      _$GetEventContextRequestFromJson(json);
+}