Provide a BackOffExecution that indicates the rate at which an operation should be retried.

Users of this interface are expected to use it like this:

BackOffExecution exec = backOff.start();

// In the operation recovery/retry loop:
long waitInterval = exec.nextBackOff();
if (waitInterval == BackOffExecution.STOP) {
    // do not retry operation
}
else {
    // sleep, e.g. Thread.sleep(waitInterval)
    // retry operation
}

Once the underlying operation has completed successfully, the execution instance can be discarded.