NIOSSHClientUserAuthenticationDelegate Improvement Request: Result Reporting

The `NIOSSHClientUserAuthenticationDelegate` provides a single method, `nextAuthenticationRequest`, for providing offers for authenticating with a remote host. In the golden path, an auth request is successful and everyone is happy. However, in situations where the request fails, either because of incorrect credentials or an unexpected failure on the remote end, it would be useful for the delegate to receive a notification to that effect. As things stand now, the only way to know an offer fails is if the method is called again. That type of inference is something I'd rather not rely upon.

In my research of this repository, I came across `NIOSSHUserAuthenticationOutcome`; I wonder if using that here would be helpful?

Start by tracing NIOSSHClientUserAuthenticationDelegate.nextAuthenticationRequest and reviewing NIOSSHUserAuthenticationOutcome to understand the existing authentication flow and available result information. Define the failure-notification semantics and the tests needed to show that incorrect credentials and remote failures are reported explicitly rather than inferred from another request.

Written by the indexing model from the issue text.