public void writeInstant(Instant instant) {
        if (instant == null) {
            writeNull();
            return;
        }

        String str = DateTimeFormatter.ISO_INSTANT.format(instant);
        writeString(str);
    }
write long value as String
@param value value
@since 2.0.49
core/src/main/java/com/alibaba/fastjson2/JSONWriter.java