Server support (stdio) (#19)

* Server support (stdio)
* TestServer project
* Refactored McpClient class to extract shared endpoint logic (with McpServer) to a base class, McpJsonRpcEndpoint.
* Improved xmldoc comments for protocol types, mirroring specification schema comments.
* Update README.MD

src/mcpdotnet/Protocol/Transport/SseClientTransportOptions.cs

@@ -0,0 +1,27 @@
+namespace McpDotNet.Protocol.Transport;
+
+/// <summary>
+/// Options for configuring the SSE transport.
+/// </summary>
+public record SseClientTransportOptions
+{
+    /// <summary>
+    /// Timeout for initial connection and endpoint event.
+    /// </summary>
+    public TimeSpan ConnectionTimeout { get; init; } = TimeSpan.FromSeconds(30);
+
+    /// <summary>
+    /// Number of reconnection attempts for SSE connection.
+    /// </summary>
+    public int MaxReconnectAttempts { get; init; } = 3;
+
+    /// <summary>
+    /// Delay between reconnection attempts.
+    /// </summary>
+    public TimeSpan ReconnectDelay { get; init; } = TimeSpan.FromSeconds(5);
+
+    /// <summary>
+    /// Headers to include in HTTP requests.
+    /// </summary>
+    public Dictionary<string, string>? AdditionalHeaders { get; init; }
+}