Additional dialogic inventory adapters

[this-is-envy]

We currently only support .has

Let's expand this to include

• .add_item(item_id: String, count: int = 1) to add one or more items,
• remove_item(item_id: String, count: int = 1) to remove one or more items,
• expand .has to have a count argument, and
• 'has_room(item_id: String, count: int) -> bool' which returns true if the player can hold new items and false if they don't have room