Creates a new RelayClient instance.

The client automatically includes an X-Relay-Client header with the platform identifier based on the target OS (e.g., "appservices-ios", "appservices-android", "appservices-macos", etc.) to help the Relay backend distinguish mobile vs desktop requests.

Parameters

• server_url: Base URL for the Relay API.

• auth_token: Optional relay-scoped access token (see struct docs).

Returns

A new `RelayClient` configured for the specified server and token.