feat: add jetstream api router and error envelope

src/NATS.Server/JetStream/Api/JetStreamApiResponse.cs

@@ -0,0 +1,46 @@
+namespace NATS.Server.JetStream.Api;
+
+public sealed class JetStreamApiResponse
+{
+    public JetStreamApiError? Error { get; init; }
+    public JetStreamStreamInfo? StreamInfo { get; init; }
+    public JetStreamConsumerInfo? ConsumerInfo { get; init; }
+
+    public static JetStreamApiResponse NotFound(string subject) => new()
+    {
+        Error = new JetStreamApiError
+        {
+            Code = 404,
+            Description = $"unknown api subject '{subject}'",
+        },
+    };
+
+    public static JetStreamApiResponse Ok() => new();
+}
+
+public sealed class JetStreamStreamInfo
+{
+    public required JetStreamStreamConfig Config { get; init; }
+    public required JetStreamStreamState State { get; init; }
+}
+
+public sealed class JetStreamConsumerInfo
+{
+    public required JetStreamConsumerConfig Config { get; init; }
+}
+
+public sealed class JetStreamStreamConfig
+{
+    public string Name { get; init; } = string.Empty;
+}
+
+public sealed class JetStreamStreamState
+{
+    public ulong Messages { get; init; }
+    public ulong FirstSeq { get; init; }
+}
+
+public sealed class JetStreamConsumerConfig
+{
+    public string DurableName { get; init; } = string.Empty;
+}