Remove timestamp rounding to avoid preliminary timer firing

[mfateev]

Cassandra timer resolution changed from seconds to milliseconds.

After timer resolution changes this rounding caused preliminary timer firing.

I tested it through Java WorkflowTest.timerTest. It was failing frequently without this fix.

[wxing1292]

@mfateev @samarabbas i suspect these 2 places may be broken due to this change

temporal/service/history/timerQueueStandbyTaskExecutor.go

Lines 132 to 135 in 50de8a2

	if isExpired := timerSequence.isExpired(
	timestamp.TimeValue(timerTask.VisibilityTime),
	timerSequenceID,
	); isExpired {

temporal/service/history/timerQueueStandbyTaskExecutor.go

Lines 190 to 192 in 50de8a2

	if isExpired := timerSequence.isExpired(
	timestamp.TimeValue(timerTask.VisibilityTime),
	timerSequenceID,

consider timerTask from above link is generated by timerSequenceID (timestamp being same)
but due to the precision loss, timerTask will be before timerSequenceID causing the isExpired function NOT return true

[wxing1292]

the comparison within the timerQueueActiveTaskExecutor is not strictly speaking correct.

temporal/service/history/timerQueueActiveTaskExecutor.go

Line 143 in 50de8a2

if expired := timerSequence.isExpired(referenceTime, timerSequenceID); !expired {

here the isExpired function is comparing the timerSequence vs "now"

say the original timer task before precision loss (before persistence to DB) is T0+0.999ms, the timer task after the precision loss is T0, now is T0+0.5ms, then the timer task which should be fired will not fire.

[wxing1292]

to solve this

temporal/common/clock/time_source.go

Line 60 in 50de8a2

return time.Now().UTC()

and

temporal/common/clock/time_source.go

Line 76 in 50de8a2

ts.now = now

must be millisecond precision