Request duration measurements aren't using a monotonic clock

[ghost]

Right now Kiev is using the difference between the return values of Time.now to calculate request duration. Instead, it should be using a process' monotonic clock as outlined in the article here: https://blog.dnsimple.com/2018/03/elapsed-time-with-ruby-the-right-way/:

To recap: system clock is constantly floating and it doesn't move only forwards. If your calculation of elapsed time is based on it, you're very likely to run into calculation errors or even outages.

At a glance I only found one place where this has to be changed:

kiev/lib/kiev/request_logger.rb

Lines 10 to 20 in 8cba28a

	began_at = Time.now
	error = nil
	begin
	return_value = yield
	rescue StandardError => e
	error = e
	end
	begin
	data[:request_duration] = ((Time.now - began_at) * 1000).round(3)

…but there may be more.