A simple Ruby command-line application for an inventory management system and billing system for a store. The application should have the following features:
- Maintain a list of items in the inventory.
- Each item should have attributes like item name, quantity, and price.
- Display the list of all items in the inventory with their quantity and price.
- Allow the user to create a new bill.
- Add items to the bill along with their quantity and price.
- Calculate and display the total price of the bill.
- Users should be able to add, remove, or update items in the inventory.
- The billing system should allow users to add multiple items to a bill.
- The application should handle errors gracefully (e.g., invalid inputs, insufficient inventory, etc.).
- Provide an option to view the final bill with the list of items and the total price.