public static StringBuilder elapsed(long elapsed, TimeUnit timeUnit) {
        final StringBuilder buf = new StringBuilder(16);
        appendElapsed(buf, timeUnit.toNanos(elapsed));
        return buf;
    }
Creates a new {@link StringBuilder} whose content is the human-readable representation of the duration
given as {@code elapsed}.
core/src/main/java/com/linecorp/armeria/common/util/TextFormatter.java