Support for virtual tags

Hello, 👋

Thanks for your work maintaining taskwarrior as well as this library :)

AFAICT, `tasklib` doesn't support virtual tags, e.g., `+TODAY`

From the command line, I get the following information:

```
Name Value
ID 735
Description kalispera
...
Tags test_gcal
Virtual tags DUE DUETODAY LATEST MONTH OVERDUE PENDING QUARTER READY TAGGED TODAY UDA UNBLOCKED WEEK YEAR
UUID ba8133fd-9b69-4c97-8141-60aeff276780
```
But exporting the data of the same task in tasklib shows the following:

```
'{"id":735,"description":"kalispera","due":"20230118T220000Z","entry":"20230119T144350Z","modified":"20230119T145926Z","status":"pending","twgcalsyncduration":"PT15M","uuid":"ba8133fd-9b69-4c97-8141-60aeff276780","tags":"test_gcal","urgency":9.92383}'
```

I'm the maintainer of [syncall](https://github.com/bergercookie/syncall) and while I'm currently using `taskw` for communicating with taskwarrior, I consider switching to `tasklib`.

This would be really useful feature to have :)

Related ticket: https://github.com/bergercookie/syncall/issues/59