default long totalDurationNanos() {
        return responseEndTimeNanos() - requestStartTimeNanos();
    }
Returns the amount of time taken since the {@link Request} processing started and until the
{@link Response} processing ended. This property is available only when both
{@link RequestLogProperty#REQUEST_START_TIME} and {@link RequestLogProperty#RESPONSE_START_TIME} are
available.

@throws RequestLogAvailabilityException if the property is not available yet.
@see RequestLogProperty#RESPONSE_END_TIME
core/src/main/java/com/linecorp/armeria/common/logging/RequestLog.java