dfr get-nanosecond for dataframe

Gets nanosecond from date.

Signature

> dfr get-nanosecond

Examples

Returns nanosecond from a date

> let dt = ('2020-08-04T16:39:18+00:00' | into datetime -z 'UTC');
    let df = ([$dt $dt] | dfr into-df);
    $df | dfr get-nanosecond
╭───┬───╮
│ # │ 0 │
├───┼───┤
│ 0 │ 0 │
│ 1 │ 0 │
╰───┴───╯