doc: update default to formatting

see https://stackoverflow.com/questions/17380701/make-sphinxs-autodoc-show-default-values-in-parameters-description

```
:param iface: Bluetooth interface number (0 = /dev/hci0) used for the
    connection, defaults to 0
:type iface: int, optional
```

<img width="852" height="302" alt="Image" src="https://github.com/user-attachments/assets/eafddbb3-3cbd-4f83-9888-4efd3151ee80" />