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.

tests/StellaOps.Router.Transport.InMemory.Tests/HelloHeartbeatFlowTests.cs

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+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Options;
+using StellaOps.Router.Common.Enums;
+using StellaOps.Router.Common.Models;
+using StellaOps.Router.Transport.InMemory;
+using Xunit;
+
+namespace StellaOps.Router.Transport.InMemory.Tests;
+
+public class HelloHeartbeatFlowTests
+{
+    private readonly InMemoryConnectionRegistry _registry;
+    private readonly InMemoryTransportServer _server;
+    private readonly InMemoryTransportClient _client;
+
+    public HelloHeartbeatFlowTests()
+    {
+        var services = new ServiceCollection();
+        services.AddLogging();
+        services.AddInMemoryTransport();
+
+        var provider = services.BuildServiceProvider();
+        _registry = provider.GetRequiredService<InMemoryConnectionRegistry>();
+        _server = provider.GetRequiredService<InMemoryTransportServer>();
+        _client = provider.GetRequiredService<InMemoryTransportClient>();
+    }
+
+    [Fact]
+    public async Task ConnectAsync_SendsHelloAndRegistersEndpoints()
+    {
+        // Arrange
+        var instance = new InstanceDescriptor
+        {
+            InstanceId = "inst-1",
+            ServiceName = "test-service",
+            Version = "1.0.0",
+            Region = "eu1"
+        };
+
+        var endpoints = new List<EndpointDescriptor>
+        {
+            new()
+            {
+                ServiceName = "test-service",
+                Version = "1.0.0",
+                Method = "GET",
+                Path = "/api/test"
+            }
+        };
+
+        // Act
+        await _server.StartAsync(CancellationToken.None);
+        await _client.ConnectAsync(instance, endpoints, CancellationToken.None);
+
+        // Assert
+        Assert.Equal(1, _registry.Count);
+        var connections = _registry.GetAllConnections();
+        Assert.Single(connections);
+        Assert.Equal("test-service", connections[0].Instance.ServiceName);
+        Assert.Equal(TransportType.InMemory, connections[0].TransportType);
+    }
+
+    [Fact]
+    public async Task SendHeartbeatAsync_SendsHeartbeatFrame()
+    {
+        // Arrange
+        var instance = new InstanceDescriptor
+        {
+            InstanceId = "inst-1",
+            ServiceName = "test-service",
+            Version = "1.0.0",
+            Region = "eu1"
+        };
+
+        await _server.StartAsync(CancellationToken.None);
+        await _client.ConnectAsync(instance, [], CancellationToken.None);
+
+        var heartbeat = new HeartbeatPayload
+        {
+            InstanceId = "inst-1",
+            Status = InstanceHealthStatus.Healthy
+        };
+
+        // Act
+        await _client.SendHeartbeatAsync(heartbeat, CancellationToken.None);
+
+        // Allow processing
+        await Task.Delay(100);
+
+        // Assert - no exception means heartbeat was sent successfully
+        Assert.Equal(1, _registry.Count);
+    }
+
+    [Fact]
+    public async Task DisconnectAsync_RemovesConnection()
+    {
+        // Arrange
+        var instance = new InstanceDescriptor
+        {
+            InstanceId = "inst-1",
+            ServiceName = "test-service",
+            Version = "1.0.0",
+            Region = "eu1"
+        };
+
+        await _server.StartAsync(CancellationToken.None);
+        await _client.ConnectAsync(instance, [], CancellationToken.None);
+        Assert.Equal(1, _registry.Count);
+
+        // Act
+        await _client.DisconnectAsync();
+
+        // Assert
+        Assert.Equal(0, _registry.Count);
+    }
+}