fix unmarshalling error for Meta property

Author: ezynda3

mcp/tools.go

@@ -504,7 +504,7 @@ func (r *CallToolResult) UnmarshalJSON(data []byte) error {
 	// Unmarshal Meta
 	if meta, ok := raw["_meta"]; ok {
 		if metaMap, ok := meta.(map[string]any); ok {
-			r.Meta = metaMap
+			r.Meta = NewMetaFromMap(metaMap)
 		}
 	}