perf: reduce SubList token string churn

src/NATS.Server/Subscriptions/SubList.cs

@@ -362,9 +362,9 @@ public sealed class SubList : IDisposable
                 }
                 else
                 {
-                    var key = token.ToString();
-                    if (!level.Nodes.TryGetValue(key, out node))
+                    if (!TryGetLiteralNode(level, token, out _, out node))
                     {
+                        var key = token.ToString();
                         node = new TrieNode();
                         level.Nodes[key] = node;
                     }
@@ -474,13 +474,20 @@ public sealed class SubList : IDisposable
             }
             else
             {
-                level.Nodes.TryGetValue(token.ToString(), out node);
+                if (!TryGetLiteralNode(level, token, out var existingToken, out node))
+                    return false;
+
+                pathList.Add((level, node, existingToken, isPwc: false, isFwc: false));
+                if (node.Next == null)
+                    return false; // corrupted trie state
+                level = node.Next;
+                continue;
             }
 
             if (node == null)
                 return false; // not found
 
-            var tokenStr = token.ToString();
+            var tokenStr = isPwc ? "*" : ">";
             pathList.Add((level, node, tokenStr, isPwc, isFwc));
             if (node.Next == null)
                 return false; // corrupted trie state
@@ -652,6 +659,23 @@ public sealed class SubList : IDisposable
         return removed;
     }
 
+    private static bool TryGetLiteralNode(TrieLevel level, ReadOnlySpan<char> token, out string existingToken, out TrieNode node)
+    {
+        foreach (var (candidate, existingNode) in level.Nodes)
+        {
+            if (!SubjectMatch.TokenEquals(token, candidate))
+                continue;
+
+            existingToken = candidate;
+            node = existingNode;
+            return true;
+        }
+
+        existingToken = string.Empty;
+        node = null!;
+        return false;
+    }
+
     private bool HasExactQueueInterestNoLock(string subject, string queue)
     {
         var subs = new List<Subscription>();

src/NATS.Server/Subscriptions/SubjectMatch.cs

@@ -249,6 +249,9 @@ public static class SubjectMatch
         return tokens.Count == test.Count;
     }
 
+    internal static bool TokenEquals(ReadOnlySpan<char> token, string candidate)
+        => token.SequenceEqual(candidate);
+
     private static bool TokensCanMatch(ReadOnlySpan<char> t1, ReadOnlySpan<char> t2)
     {
         if (t1.Length == 1 && (t1[0] == Pwc || t1[0] == Fwc))