- dynamic callback(
callback and batches any requests sent until it returns.
A batch of requests is sent in a single message on the underlying stream, and the responses are likewise sent back in a single message.
callback may be synchronous or asynchronous. If it returns a Future,
requests will be batched until that Future returns; otherwise, requests
will only be batched while synchronously executing
If this is called in the context of another withBatch call, it just
callback without creating another batch. This means that
responses are batched until the first batch ends.
@override void withBatch(Function() callback) => _client.withBatch(callback);