Allow for the ability to specify a last execution instant.

[kevincianfarini]

This will help recover from downtime within processes that are supposed to have 100% uptime.

public fun Clock.schedulePulse(
    schedule: PulseSchedule,
    timeZone: TimeZone = TimeZone.UTC,
    lastExecution: Instant = now()
): Pulse {
    val flow = flow {
        var lastPulse: LocalDateTime = lastExecution.toLocalDateTime(timeZone)
        while (true) {
            val nextPulse = lastPulse.nextMatch(schedule)
            delayUntil(nextPulse, timeZone)
            emit(nextPulse.toInstant(timeZone))
            lastPulse = nextPulse
        }
    }
    return Pulse(flow)
}