Backport PR #768: change unsupported_slash_commands default value from dict to set (#771)

Co-authored-by: michaelchia <[email protected]>

Author: meeseeksmachine

packages/jupyter-ai-magics/jupyter_ai_magics/providers.py

@@ -206,7 +206,7 @@ class Config:
     serve a custom provider and want to distinguish it in the chat UI.
     """
 
-    unsupported_slash_commands: ClassVar[set] = {}
+    unsupported_slash_commands: ClassVar[set] = set()
     """
     A set of slash commands unsupported by this provider. Unsupported slash
     commands are not shown in the help message, and cannot be used while this