feat(batch25): implement gateway reply map and inbound message pipeline

dotnet/src/ZB.MOM.NatsNet.Server/Accounts/Account.cs

@@ -358,6 +358,12 @@ public sealed partial class Account : INatsAccount
     /// </summary>
     internal byte[]? ServiceImportReply { get; set; }
 
+    /// <summary>
+    /// Gateway reply mapping table used for routed reply restoration.
+    /// Mirrors Go <c>gwReplyMapping</c>.
+    /// </summary>
+    internal GwReplyMapping GwReplyMapping { get; } = new();
+
     /// <summary>
     /// Subscription ID counter for internal use.
     /// Mirrors Go <c>isid uint64</c>.