Add a SurfaceWorkErrors() opt to the retrier

[slizco]

If the retrier encounters a context-related error, such as context.DeadlineExceeded while attempting retries of work(), the context error is returned. This means the actual error from work() never bubbles up. Because the context is often used to enforce a timeout, many callers are likely more interested in the last non-nil error returned by the work() function.

We introduce a WithSurfaceWorkErrors() option to the retrier.Retrier that when used, means the last non-nil work error will be returned even if context-related errors are encountered.