Fix loss of precision with BigDateTime

[lanfeust69]

We should ensure as much as possible a correct round-trip with DateTime. Since DateTime has a higher precision (1/10 µs instead of 1 µs), this is the limit, but we can avoid truncating microseconds.

[Ju42]

Hello @zoechelvaraj is this project still maintained ? I see that you accepted this PR a year ago but it's still waiting to be merged