@UnstableApi
    static ExponentialBackoffBuilder builderForExponential() {
        return new ExponentialBackoffBuilder();
    }
Returns an {@link ExponentialBackoffBuilder} that provides methods to configure
backoff delay which is exponentially-increasing. The default values are as follows:
<ul>
  <li>{@code initialDelayMillis}: {@value ExponentialBackoffBuilder#DEFAULT_INITIAL_DELAY_MILLIS}</li>
  <li>{@code maxDelayMillis}: {@value ExponentialBackoffBuilder#DEFAULT_MAX_DELAY_MILLIS}</li>
  <li>{@code multiplier}: {@value ExponentialBackoffBuilder#DEFAULT_MULTIPLIER}</li>
</ul>
core/src/main/java/com/linecorp/armeria/client/retry/Backoff.java