Add Operators for the relationship Volume = VolumeFlow/TimeSpan (or Duration)

e.g.
```
public partial struct Volume
{
        //...
        public static VolumeFlow operator /(Volume volume, TimeSpan timeSpan)
        {
               return VolumeFlow.FromCubicMetersPerSecond(volume.CubicMeters / timeSpan.Seconds);
        }
}
```