Implement ReturnJsonSchema in McpClientTool. (#538)

Co-authored-by: Steven Luiten <[email protected]>

Author: S-Luiten

src/ModelContextProtocol.Core/Client/McpClientTool.cs

@@ -77,6 +77,9 @@ internal McpClientTool(
     /// <inheritdoc/>
     public override JsonElement JsonSchema => ProtocolTool.InputSchema;
 
+    /// <inheritdoc/>
+    public override JsonElement? ReturnJsonSchema => ProtocolTool.OutputSchema;
+
     /// <inheritdoc/>
     public override JsonSerializerOptions JsonSerializerOptions { get; }