num_conf on get_balance

Using last lib (0.0.55)  on python3.0 installed on Ubuntu Jammy Jellyfish (or 22.04)  

```
session.get_balance({'subaccount': 0, 'num_confs': 2})
```

Generate error `num_confs must be set to 0 or 1`
Can you implement this function for `num_confs` >1?
