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

tests/NATS.Server.Tests/Gateways/GatewayRemoteConfigParityBatch3Tests.cs

@@ -0,0 +1,61 @@
+using NATS.Server.Configuration;
+
+namespace NATS.Server.Tests.Gateways;
+
+public class GatewayRemoteConfigParityBatch3Tests
+{
+    [Fact]
+    public void RemoteGatewayOptions_tracks_connection_attempts_and_implicit_flag()
+    {
+        var cfg = new RemoteGatewayOptions { Name = "GW-B", Implicit = true };
+
+        cfg.IsImplicit().ShouldBeTrue();
+        cfg.GetConnAttempts().ShouldBe(0);
+        cfg.BumpConnAttempts().ShouldBe(1);
+        cfg.BumpConnAttempts().ShouldBe(2);
+        cfg.GetConnAttempts().ShouldBe(2);
+        cfg.ResetConnAttempts();
+        cfg.GetConnAttempts().ShouldBe(0);
+    }
+
+    [Fact]
+    public void RemoteGatewayOptions_add_and_update_urls_normalize_and_deduplicate()
+    {
+        var cfg = new RemoteGatewayOptions();
+        cfg.AddUrls(["127.0.0.1:7222", "nats://127.0.0.1:7222", "nats://127.0.0.1:7223"]);
+
+        cfg.Urls.Count.ShouldBe(2);
+        cfg.Urls.ShouldContain("nats://127.0.0.1:7222");
+        cfg.Urls.ShouldContain("nats://127.0.0.1:7223");
+
+        cfg.UpdateUrls(
+            configuredUrls: ["127.0.0.1:7333"],
+            discoveredUrls: ["nats://127.0.0.1:7334", "127.0.0.1:7333"]);
+
+        cfg.Urls.Count.ShouldBe(2);
+        cfg.Urls.ShouldContain("nats://127.0.0.1:7333");
+        cfg.Urls.ShouldContain("nats://127.0.0.1:7334");
+    }
+
+    [Fact]
+    public void RemoteGatewayOptions_save_tls_hostname_and_get_urls_helpers()
+    {
+        var cfg = new RemoteGatewayOptions
+        {
+            Urls = ["127.0.0.1:7444", "nats://localhost:7445"],
+        };
+
+        cfg.SaveTlsHostname("nats://gw.example.net:7522");
+        cfg.TlsName.ShouldBe("gw.example.net");
+
+        var urlStrings = cfg.GetUrlsAsStrings();
+        urlStrings.Count.ShouldBe(2);
+        urlStrings.ShouldContain("nats://127.0.0.1:7444");
+        urlStrings.ShouldContain("nats://localhost:7445");
+
+        var urls = cfg.GetUrls();
+        urls.Count.ShouldBe(2);
+        urls.ShouldContain(u => u.Authority == "127.0.0.1:7444");
+        urls.ShouldContain(u => u.Authority == "localhost:7445");
+    }
+}