feat(batch18): implement group-a server core helpers

dotnet/src/ZB.MOM.NatsNet.Server/NatsServer.Init.cs

@@ -265,6 +265,22 @@ public sealed partial class NatsServer
         return true;
     }
 
+    /// <summary>
+    /// Returns S2 writer options for the selected route compression mode.
+    /// Mirrors Go <c>s2WriterOptions</c>.
+    /// </summary>
+    internal static string[]? S2WriterOptions(string cm)
+    {
+        var opts = new List<string> { "writer_concurrency=1" };
+        return cm switch
+        {
+            CompressionMode.S2Uncompressed => [.. opts, "writer_uncompressed"],
+            CompressionMode.S2Best => [.. opts, "writer_best_compression"],
+            CompressionMode.S2Better => [.. opts, "writer_better_compression"],
+            _ => null,
+        };
+    }
+
     // =========================================================================
     // Factory methods (features 2983–2985)
     // =========================================================================
@@ -509,20 +525,27 @@ public sealed partial class NatsServer
     /// Background loop that logs TLS rate-limited connection rejections every second.
     /// Mirrors Go <c>Server.logRejectedTLSConns</c>.
     /// </summary>
-    internal async Task LogRejectedTlsConnsAsync(CancellationToken ct)
+    internal Task LogRejectedTlsConnsAsync(CancellationToken ct) =>
+        LogRejectedTLSConns(ct);
+
+    /// <summary>
+    /// Background loop that logs TLS rate-limited connection rejections every second.
+    /// Mirrors Go <c>Server.logRejectedTLSConns</c>.
+    /// </summary>
+    internal async Task LogRejectedTLSConns(CancellationToken ct, TimeSpan? interval = null)
     {
-        using var timer = new PeriodicTimer(TimeSpan.FromSeconds(1));
+        using var timer = new PeriodicTimer(interval ?? TimeSpan.FromSeconds(1));
         while (!ct.IsCancellationRequested)
         {
-            try { await timer.WaitForNextTickAsync(ct); }
-            catch (OperationCanceledException) { break; }
-
             if (_connRateCounter is not null)
             {
                 var blocked = _connRateCounter.CountBlocked();
                 if (blocked > 0)
                     Warnf("Rejected {0} connections due to TLS rate limiting", blocked);
             }
+
+            try { await timer.WaitForNextTickAsync(ct); }
+            catch (OperationCanceledException) { break; }
         }
     }