chg/fix(notifications): use tanstack as source of truth for optimistic updating, simplifies source

[synoet]

• Uses tanstack data as the source of truth for optimistic inserts and removes with the ws
• notification-source becomes alot simpler. just derive data from the query data and group it by composite key.
• updates helpers

This fixes some issues I was seeing in dev where notification reconciling was incorrect due to how we handle optimistic remove on tanstack.
This is a move in the right direction anyway.

Next Steps:

• Websocket invalidation / optimistic updating of notifications should happen in the query package.
• Once this happens notification-source can be drastically simplified and maybe even removed.