truncate overflows when handling times in milliseconds

[matsjoyce]

Same issue as #591 (tracked in #721). I am receiving a bunch of timestamps from an API as floating point seconds since the epoch. To process them I was doing:

Time.millisToPosix <| truncate <| t * 1000

which causes an overflow, giving times before 1970. Changing to:

Time.millisToPosix <| round <| t * 1000

fixed the issue, as would using ceiling. However, it would be nice if truncate could handle 64 bit floats without surprises.

[github-actions]

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