RetryPolicy
Decides whether (and after how long) a failed request should be retried.
Implement this to plug in custom retry behavior. NetworkClient consults it after every failed attempt: returning a non-negative delay schedules another attempt after that many milliseconds; returning null stops retrying and propagates the error.
The default, DefaultRetryPolicy, retries transient failures with jittered exponential backoff. Use RetryPolicy.None to disable retries entirely.