CupertinoClient close method doesn't close the connection

[veloce]

CupertinoClient doesn't close the underlying connection when calling close() on it. It will just prevent sending further requests.

It is an issue because a persistent connection won't be closed, and we have no way to cancel a pending request.

Also it is not consistent with the behaviour of IOClient, which does close the connection.

[brianquinlan]

This is interesting:
https://lapcatsoftware.com/articles/NSURLSession.html
https://developer.apple.com/documentation/foundation/nsurlsession/1411538-invalidateandcancel