feat: implement full MQTT Go parity across 5 phases — binary protocol, auth/TLS, cross-protocol bridging, monitoring, and JetStream persistence

Phase 1: Binary MQTT 3.1.1 wire protocol with PipeReader-based parsing,
full packet type dispatch, and MQTT 3.1.1 compliance checks.

Phase 2: Auth pipeline routing MQTT CONNECT through AuthService,
TLS transport with SslStream wrapping, pinned cert validation.

Phase 3: IMessageRouter refactor (NatsClient → INatsClient),
MqttNatsClientAdapter for cross-protocol bridging, MqttTopicMapper
with full Go-parity topic/subject translation.

Phase 4: /connz mqtt_client field population, /varz actual MQTT port.

Phase 5: JetStream persistence — MqttStreamInitializer creates 5
internal streams, MqttConsumerManager for QoS 1/2 consumers,
subject-keyed session/retained lookups replacing linear scans.

All 503 MQTT tests and 1589 Core tests pass.

tests/NATS.Server.Mqtt.Tests/Mqtt/MqttRetainedMessageParityTests.cs

@@ -17,6 +17,7 @@ public class MqttRetainedMessageParityTests
     public async Task Retained_message_not_delivered_when_subscriber_connects_after_publish()
     {
         await using var listener = new MqttListener("127.0.0.1", 0);
+        listener.UseBinaryProtocol = false;
         using var cts = new CancellationTokenSource();
         await listener.StartAsync(cts.Token);
 
@@ -44,6 +45,7 @@ public class MqttRetainedMessageParityTests
     public async Task Non_retained_publish_delivers_to_existing_subscriber()
     {
         await using var listener = new MqttListener("127.0.0.1", 0);
+        listener.UseBinaryProtocol = false;
         using var cts = new CancellationTokenSource();
         await listener.StartAsync(cts.Token);
 
@@ -71,6 +73,7 @@ public class MqttRetainedMessageParityTests
     public async Task Live_message_delivered_to_existing_subscriber_is_not_flagged_retained()
     {
         await using var listener = new MqttListener("127.0.0.1", 0);
+        listener.UseBinaryProtocol = false;
         using var cts = new CancellationTokenSource();
         await listener.StartAsync(cts.Token);
 
@@ -98,6 +101,7 @@ public class MqttRetainedMessageParityTests
     public async Task Multiple_publishers_deliver_to_same_subscriber()
     {
         await using var listener = new MqttListener("127.0.0.1", 0);
+        listener.UseBinaryProtocol = false;
         using var cts = new CancellationTokenSource();
         await listener.StartAsync(cts.Token);
 
@@ -133,6 +137,7 @@ public class MqttRetainedMessageParityTests
     public async Task Message_payload_is_not_corrupted_through_broker()
     {
         await using var listener = new MqttListener("127.0.0.1", 0);
+        listener.UseBinaryProtocol = false;
         using var cts = new CancellationTokenSource();
         await listener.StartAsync(cts.Token);
 
@@ -161,6 +166,7 @@ public class MqttRetainedMessageParityTests
     public async Task Sequential_publishes_all_deliver()
     {
         await using var listener = new MqttListener("127.0.0.1", 0);
+        listener.UseBinaryProtocol = false;
         using var cts = new CancellationTokenSource();
         await listener.StartAsync(cts.Token);
 
@@ -190,6 +196,7 @@ public class MqttRetainedMessageParityTests
     public async Task Multiple_topics_receive_messages_independently()
     {
         await using var listener = new MqttListener("127.0.0.1", 0);
+        listener.UseBinaryProtocol = false;
         using var cts = new CancellationTokenSource();
         await listener.StartAsync(cts.Token);
 
@@ -230,6 +237,7 @@ public class MqttRetainedMessageParityTests
     public async Task Subscriber_reconnect_resubscribe_receives_new_messages()
     {
         await using var listener = new MqttListener("127.0.0.1", 0);
+        listener.UseBinaryProtocol = false;
         using var cts = new CancellationTokenSource();
         await listener.StartAsync(cts.Token);