[REFACTOR] `network_manager` missing helpful methods

Best to add these at some point soon

- `is_connected()` - check if any network is connected
- `current_network()` - get full `Network` object for current connection
- `disconnect()` - disconnect from current network (not just VPN)
- `list_saved_connections()` - list all saved connection profiles
- `get_device_by_interface(name: &str)` - find device by name