Implement InMemory Transport Layer for StellaOps Router

- Added InMemoryTransportOptions class for configuration settings including timeouts and latency.
- Developed InMemoryTransportServer class to handle connections, frame processing, and event management.
- Created ServiceCollectionExtensions for easy registration of InMemory transport services.
- Established project structure and dependencies for InMemory transport library.
- Implemented comprehensive unit tests for endpoint discovery, connection management, request/response flow, and streaming capabilities.
- Ensured proper handling of cancellation, heartbeat, and hello frames within the transport layer.

src/__Libraries/StellaOps.Router.Common/Abstractions/IGlobalRoutingState.cs

@@ -0,0 +1,31 @@
+using StellaOps.Router.Common.Models;
+
+namespace StellaOps.Router.Common.Abstractions;
+
+/// <summary>
+/// Provides global routing state derived from all live connections.
+/// </summary>
+public interface IGlobalRoutingState
+{
+    /// <summary>
+    /// Resolves an HTTP request to an endpoint descriptor.
+    /// </summary>
+    /// <param name="method">The HTTP method.</param>
+    /// <param name="path">The request path.</param>
+    /// <returns>The endpoint descriptor, or null if not found.</returns>
+    EndpointDescriptor? ResolveEndpoint(string method, string path);
+
+    /// <summary>
+    /// Gets all connections that can handle the specified endpoint.
+    /// </summary>
+    /// <param name="serviceName">The service name.</param>
+    /// <param name="version">The service version.</param>
+    /// <param name="method">The HTTP method.</param>
+    /// <param name="path">The request path.</param>
+    /// <returns>The available connection states.</returns>
+    IReadOnlyList<ConnectionState> GetConnectionsFor(
+        string serviceName,
+        string version,
+        string method,
+        string path);
+}

src/__Libraries/StellaOps.Router.Common/Abstractions/IRegionProvider.cs

@@ -0,0 +1,17 @@
+namespace StellaOps.Router.Common.Abstractions;
+
+/// <summary>
+/// Provides region information for routing decisions.
+/// </summary>
+public interface IRegionProvider
+{
+    /// <summary>
+    /// Gets the current gateway region.
+    /// </summary>
+    string Region { get; }
+
+    /// <summary>
+    /// Gets the neighbor regions in order of preference.
+    /// </summary>
+    IReadOnlyList<string> NeighborRegions { get; }
+}

src/__Libraries/StellaOps.Router.Common/Abstractions/IRoutingPlugin.cs

@@ -0,0 +1,19 @@
+using StellaOps.Router.Common.Models;
+
+namespace StellaOps.Router.Common.Abstractions;
+
+/// <summary>
+/// Provides extensibility for routing decisions.
+/// </summary>
+public interface IRoutingPlugin
+{
+    /// <summary>
+    /// Chooses an instance for the routing context.
+    /// </summary>
+    /// <param name="context">The routing context.</param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>The routing decision, or null if this plugin cannot decide.</returns>
+    Task<RoutingDecision?> ChooseInstanceAsync(
+        RoutingContext context,
+        CancellationToken cancellationToken);
+}

src/__Libraries/StellaOps.Router.Common/Abstractions/ITransportClient.cs

@@ -0,0 +1,51 @@
+using StellaOps.Router.Common.Models;
+
+namespace StellaOps.Router.Common.Abstractions;
+
+/// <summary>
+/// Represents a transport client for sending requests to microservices.
+/// </summary>
+public interface ITransportClient
+{
+    /// <summary>
+    /// Sends a request and waits for a response.
+    /// </summary>
+    /// <param name="connection">The connection to use.</param>
+    /// <param name="requestFrame">The request frame.</param>
+    /// <param name="timeout">The timeout for the request.</param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>The response frame.</returns>
+    Task<Frame> SendRequestAsync(
+        ConnectionState connection,
+        Frame requestFrame,
+        TimeSpan timeout,
+        CancellationToken cancellationToken);
+
+    /// <summary>
+    /// Sends a cancellation request.
+    /// </summary>
+    /// <param name="connection">The connection to use.</param>
+    /// <param name="correlationId">The correlation ID of the request to cancel.</param>
+    /// <param name="reason">Optional reason for cancellation.</param>
+    Task SendCancelAsync(
+        ConnectionState connection,
+        Guid correlationId,
+        string? reason = null);
+
+    /// <summary>
+    /// Sends a streaming request and processes the streaming response.
+    /// </summary>
+    /// <param name="connection">The connection to use.</param>
+    /// <param name="requestHeader">The request header frame.</param>
+    /// <param name="requestBody">The request body stream.</param>
+    /// <param name="readResponseBody">Callback to read the response body stream.</param>
+    /// <param name="limits">Payload limits to enforce.</param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    Task SendStreamingAsync(
+        ConnectionState connection,
+        Frame requestHeader,
+        Stream requestBody,
+        Func<Stream, Task> readResponseBody,
+        PayloadLimits limits,
+        CancellationToken cancellationToken);
+}

src/__Libraries/StellaOps.Router.Common/Abstractions/ITransportServer.cs

@@ -0,0 +1,19 @@
+namespace StellaOps.Router.Common.Abstractions;
+
+/// <summary>
+/// Represents a transport server that accepts connections from microservices.
+/// </summary>
+public interface ITransportServer
+{
+    /// <summary>
+    /// Starts listening for incoming connections.
+    /// </summary>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    Task StartAsync(CancellationToken cancellationToken);
+
+    /// <summary>
+    /// Stops accepting new connections.
+    /// </summary>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    Task StopAsync(CancellationToken cancellationToken);
+}