Add serialization roundtrip tests for all Protocol namespace types (#1289)

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Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

tests/ModelContextProtocol.Tests/Protocol/ListTasksRequestParamsTests.cs

@@ -0,0 +1,25 @@
+using ModelContextProtocol.Protocol;
+using System.Text.Json;
+
+namespace ModelContextProtocol.Tests.Protocol;
+
+public static class ListTasksRequestParamsTests
+{
+    [Fact]
+    public static void ListTasksRequestParams_SerializationRoundTrip()
+    {
+        // Arrange
+        var original = new ListTasksRequestParams
+        {
+            Cursor = "cursor-abc123"
+        };
+
+        // Act
+        string json = JsonSerializer.Serialize(original, McpJsonUtilities.DefaultOptions);
+        var deserialized = JsonSerializer.Deserialize<ListTasksRequestParams>(json, McpJsonUtilities.DefaultOptions);
+
+        // Assert
+        Assert.NotNull(deserialized);
+        Assert.Equal(original.Cursor, deserialized.Cursor);
+    }
+}