Make McpJsonUtilities public and remove IVT to sample (#5)

Also adds in the same encoder used by AIJsonUtilities.

src/ModelContextProtocol/Protocol/Transport/HttpListenerSseServerTransport.cs

@@ -42,7 +42,7 @@ public sealed class HttpListenerSseServerTransport : TransportBase, IServerTrans
     {
         _serverName = serverName;
         _logger = loggerFactory.CreateLogger<HttpListenerSseServerTransport>();
-        _jsonOptions = JsonSerializerOptionsExtensions.DefaultOptions;
+        _jsonOptions = McpJsonUtilities.DefaultOptions;
         _httpServerProvider = new HttpListenerServerProvider(port);
     }
 

src/ModelContextProtocol/Protocol/Transport/SseClientTransport.cs

@@ -65,7 +65,7 @@ public sealed class SseClientTransport : TransportBase, IClientTransport
         _httpClient = httpClient;
         _connectionCts = new CancellationTokenSource();
         _logger = (ILogger?)loggerFactory?.CreateLogger<SseClientTransport>() ?? NullLogger.Instance;
-        _jsonOptions = JsonSerializerOptionsExtensions.DefaultOptions;
+        _jsonOptions = McpJsonUtilities.DefaultOptions;
         _connectionEstablished = new TaskCompletionSource<bool>();
         _ownsHttpClient = ownsHttpClient;
     }

src/ModelContextProtocol/Protocol/Transport/StdioClientTransport.cs

@@ -43,7 +43,7 @@ public sealed class StdioClientTransport : TransportBase, IClientTransport
         _options = options;
         _serverConfig = serverConfig;
         _logger = (ILogger?)loggerFactory?.CreateLogger<StdioClientTransport>() ?? NullLogger.Instance;
-        _jsonOptions = JsonSerializerOptionsExtensions.DefaultOptions;
+        _jsonOptions = McpJsonUtilities.DefaultOptions;
     }
 
     /// <inheritdoc/>

src/ModelContextProtocol/Protocol/Transport/StdioServerTransport.cs

@@ -21,7 +21,7 @@ public sealed class StdioServerTransport : TransportBase, IServerTransport
     private readonly string _serverName;
     private readonly ILogger _logger;
 
-    private readonly JsonSerializerOptions _jsonOptions = JsonSerializerOptionsExtensions.DefaultOptions;
+    private readonly JsonSerializerOptions _jsonOptions = McpJsonUtilities.DefaultOptions;
     private readonly TextReader _stdin = Console.In;
     private readonly TextWriter _stdout = Console.Out;