Monotonic timestamp generator. Guarantees monotonicity of timestamps.
If system clock will not provide an increased timestamp, then the timestamp will
be artificially increased. If the config is provided and the clock skew is bigger than
warning_threshold (by default 1 second), then the user will be warned about
the skew repeatedly, with warning_interval provided in the settings (by default 1 second).
Remember that this generator only guarantees monotonicity within one instance of this struct!
If you create multiple instances the monotonicity guarantee becomes void.