feat: add RTT tracking and first-PING delay to NatsClient

src/NATS.Server/Monitoring/ConnzHandler.cs

@@ -30,6 +30,7 @@ public sealed class ConnzHandler(NatsServer server)
             SortOpt.ByLast => connInfos.OrderByDescending(c => c.LastActivity).ToList(),
             SortOpt.ByIdle => connInfos.OrderByDescending(c => now - c.LastActivity).ToList(),
             SortOpt.ByUptime => connInfos.OrderByDescending(c => now - c.Start).ToList(),
+            SortOpt.ByRtt => connInfos.OrderBy(c => c.Rtt).ToList(),
             _ => connInfos.OrderBy(c => c.Cid).ToList(),
         };
 
@@ -73,6 +74,7 @@ public sealed class ConnzHandler(NatsServer server)
             Reason = client.CloseReason.ToReasonString(),
             TlsVersion = client.TlsState?.TlsVersion ?? "",
             TlsCipherSuite = client.TlsState?.CipherSuite ?? "",
+            Rtt = client.Rtt == TimeSpan.Zero ? "" : $"{client.Rtt.TotalMilliseconds:F3}ms",
         };
 
         if (opts.Subscriptions)
@@ -116,6 +118,7 @@ public sealed class ConnzHandler(NatsServer server)
                 "last" => SortOpt.ByLast,
                 "idle" => SortOpt.ByIdle,
                 "uptime" => SortOpt.ByUptime,
+                "rtt" => SortOpt.ByRtt,
                 _ => SortOpt.ByCid,
             };
         }