All collection items are guaranteed to have:
- a unique `item_object_id`: this is the id of the collection item in the database
- an `item_id`: this is the id on the Hub of the underlying item (model, dataset, Space, paper); it is not necessarily unique, and only the `item_id`/`item_type` pair is unique
- an `item_type`: model, dataset, Space, paper
- the `position` of the item in the collection, which can be updated to reorganize your collection (see [`update_collection_item`] below)