Add AspNetCoreSseServer sample (#81)

* Add AspNetCoreSseMcpTransport sample

* Fix build errors after rebase

* React to McpServerFactory changes

* Make Utf8JsonWriter non thread static

* Fix test errors caused by not rebasing the HttpLister changes on factory overhaul commit

samples/AspNetCoreSseServer/Tools/EchoTool.cs

@@ -0,0 +1,14 @@
+using McpDotNet.Server;
+using System.ComponentModel;
+
+namespace TestServerWithHosting.Tools;
+
+[McpToolType]
+public static class EchoTool
+{
+    [McpTool, Description("Echoes the input back to the client.")]
+    public static string Echo(string message)
+    {
+        return "hello " + message;
+    }
+}

samples/AspNetCoreSseServer/Tools/SampleLlmTool.cs

@@ -0,0 +1,51 @@
+using McpDotNet.Protocol.Types;
+using McpDotNet.Server;
+using System.ComponentModel;
+
+namespace TestServerWithHosting.Tools;
+
+/// <summary>
+/// This tool uses depenency injection and async method
+/// </summary>
+[McpToolType]
+public class SampleLlmTool
+{
+    private readonly IMcpServer _server;
+
+    public SampleLlmTool(IMcpServer server)
+    {
+        _server = server ?? throw new ArgumentNullException(nameof(server));
+    }
+
+    [McpTool("sampleLLM"), Description("Samples from an LLM using MCP's sampling feature")]
+    public async Task<string> SampleLLM(
+        [Description("The prompt to send to the LLM")] string prompt,
+        [Description("Maximum number of tokens to generate")] int maxTokens,
+        CancellationToken cancellationToken)
+    {
+        var samplingParams = CreateRequestSamplingParams(prompt ?? string.Empty, "sampleLLM", maxTokens);
+        var sampleResult = await _server.RequestSamplingAsync(samplingParams, cancellationToken);
+
+        return $"LLM sampling result: {sampleResult.Content.Text}";
+    }
+
+    private static CreateMessageRequestParams CreateRequestSamplingParams(string context, string uri, int maxTokens = 100)
+    {
+        return new CreateMessageRequestParams()
+        {
+            Messages = [new SamplingMessage()
+                {
+                    Role = Role.User,
+                    Content = new Content()
+                    {
+                        Type = "text",
+                        Text = $"Resource {uri} context: {context}"
+                    }
+                }],
+            SystemPrompt = "You are a helpful test server.",
+            MaxTokens = maxTokens,
+            Temperature = 0.7f,
+            IncludeContext = ContextInclusion.ThisServer
+        };
+    }
+}