fix: clamp Time millisecond to a valid maximum of 999

[spokodev]

constrainTime clamps the millisecond field with
Math.max(0, Math.min(time.millisecond, 1000)), but a valid millisecond is in
the range 0 to 999. An out of range value is clamped to 1000, which is not a
representable millisecond.

constrainTime runs in the Time constructor, in .set({millisecond}), and in
copy(). So new Time(1, 2, 3, 5000).millisecond returns 1000, and
new Time(1, 2, 3, 5000).toString() returns "01:02:03" with the fraction
silently dropped, because the string builder computes String(1000 / 1000).

The fix clamps to 999, matching the sibling clamps in the same function
(seconds to 59, minutes to 59, hours to 23) and cycleTime, which already bounds
the millisecond with 0 to 999.

[snowystinger]

Thanks for the PR, added a few more tests