register method
Configures the SIP account credentials and server settings.
This method sets up the SIP user credentials but does not register with the server. Call registerServer after this to complete registration.
Parameters:
account: The SIP account configuration containing credentials and server info
Returns 0 on success, negative error code on failure.
Implementation
Future<int> register({required SipAccount account}) async {
throw UnimplementedError('register has not been implemented.');
}