`time_unit` and `time_zone` parameters in `Timestamp` `DataType`

### Is your feature request related to a problem?

If I have
```
data_type = daft.DataType.timestamp('ms', None)
```
then how can I get the time unit and time zone out?

### Describe the solution you'd like

```
data_type.time_unit
data_type.time_zone
```

### Describe alternatives you've considered

_No response_

### Additional Context

narwhals

### Would you like to implement a fix?

No