influxdb3_client: no request timeout and no way to configure one

- `Client::new` builds its HTTP client with no timeout of any kind and exposes no knob to set one; a request to a server that accepts the connection but never responds awaits forever.
- Ask: a sensible default request timeout and/or a builder option to configure it.

Start at `influxdb3_client`'s `Client::new`, where the HTTP client is built without a timeout. Trace how requests are issued and identify the relevant client tests or test entry points; done means a nonresponsive server no longer waits forever and the timeout behavior or configuration is covered.

Written by the indexing model from the issue text.