Fix E2E test gaps and add comprehensive E2E + parity test suites

- Fix pull consumer fetch: send original stream subject in HMSG (not inbox)
  so NATS client distinguishes data messages from control messages
- Fix MaxAge expiry: add background timer in StreamManager for periodic pruning
- Fix JetStream wire format: Go-compatible anonymous objects with string enums,
  proper offset-based pagination for stream/consumer list APIs
- Add 42 E2E black-box tests (core messaging, auth, TLS, accounts, JetStream)
- Add ~1000 parity tests across all subsystems (gaps closure)
- Update gap inventory docs to reflect implementation status

src/NATS.Server/Configuration/NatsConfLexer.cs

@@ -1,6 +1,10 @@
 // Port of Go conf/lex.go — state-machine tokenizer for NATS config files.
 // Reference: golang/nats-server/conf/lex.go
 
+using System.Buffers;
+using System.Globalization;
+using System.Text;
+
 namespace NATS.Server.Configuration;
 
 public sealed class NatsConfLexer
@@ -145,16 +149,23 @@ public sealed class NatsConfLexer
             return Eof;
         }
 
-        if (_input[_pos] == '\n')
+        var span = _input.AsSpan(_pos);
+        var status = Rune.DecodeFromUtf16(span, out var rune, out var consumed);
+        if (status != OperationStatus.Done || consumed <= 0)
+        {
+            consumed = 1;
+            rune = new Rune(_input[_pos]);
+        }
+
+        if (rune.Value == '\n')
         {
             _line++;
             _lstart = _pos;
         }
 
-        var c = _input[_pos];
-        _width = 1;
-        _pos += _width;
-        return c;
+        _width = consumed;
+        _pos += consumed;
+        return rune.IsBmp ? (char)rune.Value : '\uFFFD';
     }
 
     private void Ignore()
@@ -186,6 +197,20 @@ public sealed class NatsConfLexer
         return null;
     }
 
+    private LexState? Errorf(string format, params object?[] args)
+    {
+        if (args.Length == 0)
+            return Errorf(format);
+
+        var escapedArgs = new object?[args.Length];
+        for (var i = 0; i < args.Length; i++)
+        {
+            escapedArgs[i] = args[i] is char c ? EscapeSpecial(c) : args[i];
+        }
+
+        return Errorf(string.Format(CultureInfo.InvariantCulture, format, escapedArgs));
+    }
+
     // --- Helper methods ---
 
     private static bool IsWhitespace(char c) => c is '\t' or ' ';
@@ -1476,9 +1501,8 @@ public sealed class NatsConfLexer
         var r = lx.Peek();
         if (IsNL(r) || r == Eof)
         {
-            // Consume the comment text but don't emit it as a user-visible token.
-            // Just ignore it and pop back.
-            lx.Ignore();
+            // Match Go behavior: emit comment body as a text token.
+            lx.Emit(TokenType.Text);
             return lx.Pop();
         }