The cron configuration presented on the `#oban` slack channel the following:

```elixir
{"0 0 */1 * *", Worker.MarkerScheduler}
```

That configuration produced an `ArgumentError` exception while Oban tried to
expand the parsed result by `nimble_parsec` saying that we got an `Unexpected
value 1 outside of range 1..31`.

The job executor mixed native and microsecond time units, which yielded
incorrect durations. This change ensures that both `duration` and
`queue_time` values are reported using native time units while also
ensuring they are logged as microseconds by default.

Using :native works, but it isn't listed as a valid value for
the System.time_unit() type, so dialyzer complained.