public FibonacciBackoffBuilder initialDelayMillis(long initialDelayMillis) {
        checkArgument(initialDelayMillis >= 0,
                      "initialDelayMillis: %s (expected: >= 0)", initialDelayMillis);

        this.initialDelayMillis = initialDelayMillis;
        return this;
    }
Sets the initial delay in milliseconds for the Fibonacci {@link Backoff}.

<p>The initial delay is the base value from which the Fibonacci sequence will start,
and it determines the delay before the first retry.</p>

@param initialDelayMillis the initial delay in milliseconds
core/src/main/java/com/linecorp/armeria/client/retry/FibonacciBackoffBuilder.java