fix: add the missing default None value for cocoindex.init() (#527)

Author: badmonster0

python/cocoindex/lib.py

@@ -12,7 +12,7 @@
 from .convert import dump_engine_object
 
 
-def init(settings: setting.Settings | None):
+def init(settings: setting.Settings | None = None):
     """
     Initialize the cocoindex library.