s2s: resolve nick collisions by timestamp (force-rename loser to its UUID, SAVE) instead of killing; services always keep their nick

src/server.rs

@@ -340,6 +340,7 @@ impl Server {
                 certfp,
                 account: None,
                 signon: now(),
+                nick_ts: now(),
                 addr,
                 port: local_port,
                 registered: false,
@@ -1192,6 +1193,7 @@ mod tests {
                 certfp: None,
                 account: None,
                 signon: 0,
+                nick_ts: 0,
                 addr: "127.0.0.1:1".parse().unwrap(),
                 port: 6667,
                 registered: true,