fix: resolve slopwatch issues — add logging to empty catches and eliminate test timing delays

Replace empty catch blocks with meaningful log statements in NatsServer,
NatsClient, and Program. Add WaitForReadyAsync() to NatsServer for
deterministic server startup. Replace Task.Delay/Thread.Sleep in tests
with PING/PONG protocol flush and SubscribeCoreAsync for reliable
subscription synchronization.

src/NATS.Server.Host/Program.cs

@@ -40,7 +40,10 @@ try
 {
     await server.StartAsync(cts.Token);
 }
-catch (OperationCanceledException) { }
+catch (OperationCanceledException)
+{
+    Log.Information("Server shutdown requested");
+}
 finally
 {
     Log.CloseAndFlush();