bug: epoch calculation is incorrect
### Problem
Epoch calculation is wrong. Tested both in Fedora and WSL.

### To reproduce
```nim
import chronos
from std/times import epochTime

echo epochTime()
echo fastEpochTime()
echo Moment.now()
```

Outputs
```
1723049288.989397  # epochTime (seconds)
24664910  # fastEpochTime (milliseconds)
24664910171187ns  # Moment.now (nanoseconds)
```

### Expected behavior
Epoch calculation from chronos should be consistent with `std/times`' `epochTime()`.

### Versions
Nim: 2.0.8 and 1.6.20
Chronos: 4.0.0 and 4.0.2