Add a .close() method to the client

[idan3]

Why there is no close method to the client?
httpx has one and the generated client uses httpx client.

[dbanty]

Mostly because folks are expected to either use this in a context manager or use it in a form that doesn't require closing (like a one-off script). You can achieve this today by calling .get_httpx_client().close() or .get_async_httpx_client().close() as appropriate.

That said, I wouldn't be opposed to a PR which adds a .close() method to make it easier.