round method Null safety
The integer closest to this number.
Rounds away from zero when there is no closest integer:
(3.5).round() == 4 and
(-3.5).round() == -4.
The number must be finite (see isFinite).
If the value is greater than the highest representable positive integer, the result is that highest positive integer. If the value is smaller than the highest representable negative integer, the result is that highest negative integer.