Fix multiplexer importing from wrong package (#7015)

haystack/components/others/multiplexer.py

@@ -3,8 +3,8 @@
 from typing import Any, Dict
 
 from haystack import component, default_from_dict, default_to_dict
-from haystack.components.routers.conditional_router import deserialize_type, serialize_type
 from haystack.core.component.types import Variadic
+from haystack.utils.type_serialization import deserialize_type, serialize_type
 
 if sys.version_info < (3, 10):
     from typing_extensions import TypeAlias