refactor: extract NATS.Server.Monitoring.Tests project

Move 39 monitoring, events, and system endpoint test files from
NATS.Server.Tests into a dedicated NATS.Server.Monitoring.Tests project.
Update namespaces, replace private GetFreePort/ReadUntilAsync with
TestUtilities shared helpers, add InternalsVisibleTo, and register
in the solution file. All 439 tests pass.

tests/NATS.Server.Monitoring.Tests/Monitoring/ConnzParityFieldTests.cs

@@ -0,0 +1,54 @@
+using System.Text.Json;
+using System.Text;
+
+namespace NATS.Server.Monitoring.Tests;
+
+public class ConnzParityFieldTests
+{
+    [Fact]
+    public async Task Connz_includes_identity_tls_and_proxy_parity_fields()
+    {
+        await using var fx = await MonitoringParityFixture.StartAsync();
+        var jwt = BuildJwt("UISSUER", ["team:core", "tier:gold"]);
+        await fx.ConnectClientAsync("proxy:edge", "orders.created", jwt);
+
+        var connz = fx.GetConnz("?subs=detail&auth=true");
+        connz.Conns.ShouldNotBeEmpty();
+        var conn = connz.Conns.Single(c => c.AuthorizedUser == "proxy:edge");
+        conn.Proxy.ShouldNotBeNull();
+        conn.Proxy.Key.ShouldBe("edge");
+        conn.Jwt.ShouldBe(jwt);
+        conn.IssuerKey.ShouldBe("UISSUER");
+        conn.Tags.ShouldContain("team:core");
+
+        var json = JsonSerializer.Serialize(connz);
+        json.ShouldContain("tls_peer_cert_subject");
+        json.ShouldContain("tls_peer_certs");
+        json.ShouldContain("issuer_key");
+        json.ShouldContain("\"tags\"");
+        json.ShouldContain("proxy");
+        json.ShouldNotContain("jwt_issuer_key");
+    }
+
+    private static string BuildJwt(string issuer, string[] tags)
+    {
+        static string B64Url(string json)
+        {
+            return Convert.ToBase64String(Encoding.UTF8.GetBytes(json))
+                .TrimEnd('=')
+                .Replace('+', '-')
+                .Replace('/', '_');
+        }
+
+        var header = B64Url("{\"alg\":\"none\",\"typ\":\"JWT\"}");
+        var payload = B64Url(JsonSerializer.Serialize(new
+        {
+            iss = issuer,
+            nats = new
+            {
+                tags,
+            },
+        }));
+        return $"{header}.{payload}.eA";
+    }
+}