@Override
    Backoff doBuild() {
        return new ExponentialBackoff(initialDelayMillis, maxDelayMillis, multiplier);
    }
Sets the multiplier for the Exponential {@link Backoff}.

<p>The multiplier controls how much the delay increases after each retry.
The delay for each retry is determined by multiplying the previous delay by this value,
until the maximum delay is reached.</p>

@param multiplier the multiplier for the exponential backoff
core/src/main/java/com/linecorp/armeria/client/retry/ExponentialBackoffBuilder.java