When specifying the time of an event, the time should be sent to Mixpanel with millisecond accuracy

[Kas-code]

When sending an event to Mixpanel, we can optionally include the time in the event properties. This is useful for reporting events that happened in the past.

Currently, using this nuget package, times are not reported to Mixpanel using millisecond accuracy when including the time in the event properties, which can cause issues with the correct ordering of events in flow reports if events happen within the same second.

Mixpanel does support millisecond accuracy for events, see the following articles:

https://engineering.mixpanel.com/tracking-events-at-milli-second-granularity-7d1fc7f29e31
https://docs.mixpanel.com/changelogs/2022-11-07-millisecond

All that should need to be changed to support this is to change the MixpanelDateFormat in Mixpanel.Parsers.TimeParser