Make sure documentation on CancellationToken vs. Timeout is consistent between API/implementation/docs

Related to 

NCBC-3572

The interactions between Timeout and CancellationToken can be complicated and non-intuitive from a user perspective.  The Timeout includes all retries, not individual attempts.  The CancellationToken may or may not be an actual timeout.

Using CancellationTokens is a standard practice in .NET, and assuming OperationCancellationExceptions are because of timeouts is a common error.

This needs to be consistent in the SDK and clear to the user, especially what happens when specifying both a Timeout and a CancellationToken.

Additionally, once the SDK gives priority to one of Timeout or CancellationToken, do we need to let the user un-set Timeout.