Function served 

fn served(
    lasting: &mut Lasting,
    asked: &Receiver<Change>,
    on_action: &dyn Fn(&str),
    connection: &LocalConnection,
) -> Served

A lasting notification on connection: what Sioul asks shown, what the server says heard, until it is taken away or the connection is lost. Each Notify goes without waiting, its answer heard as it comes: while one is not answered, none other is sent, so that a server answering late never shows it twice (each shown with no number to replace, neither taken away: review of battery part C, L1); its late answer gives the number, and what changed meanwhile goes in its place.