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/Auth/NKeyUser.cs

@@ -6,4 +6,7 @@ public sealed class NKeyUser
     public Permissions? Permissions { get; init; }
     public string? Account { get; init; }
     public string? SigningKey { get; init; }
+    public DateTimeOffset? Issued { get; init; }
+    public IReadOnlySet<string>? AllowedConnectionTypes { get; init; }
+    public bool ProxyRequired { get; init; }
 }