[REFACTOR] `network_manager` missing helpful methods

[cachebag]

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