@Override
    public ArmeriaResteasyClientBuilder httpEngine(ClientHttpEngine httpEngine) {
        // we'll always use an embedded ArmeriaJaxrsClientEngine
        throw new UnsupportedOperationException();
    }
{@link ArmeriaJaxrsClientEngine} will always be set as an {@link ClientHttpEngine}.
@throws UnsupportedOperationException always
resteasy/src/main/java/com/linecorp/armeria/client/resteasy/ArmeriaResteasyClientBuilder.java