long nextMaxInterval() {
            long interval = (long) (period * Math.pow(1.5, attempt - 1));
            return Math.min(interval, maxPeriod);
        }
Calculates the time interval to a retry attempt. <br>
The interval increases exponentially with each attempt, at a rate of nextInterval *= 1.5
(where 1.5 is the backoff factor), to the maximum interval.

@return time in milliseconds from now until the next attempt.
shenyu-sdk/shenyu-sdk-core/src/main/java/org/apache/shenyu/sdk/core/retry/Retryer.java