Major Update for EnchantmentExtractor

New Features and Improvements:

1. XP Cost System:
- Added calculateXPCost function for dynamic XP cost calculation.
- Cost varies based on operation type (extraction or application) and number of existing enchantments.
- Implemented formula: cost * (2 ^ number_of_existing_enchantments) for progressive balancing.

2. Enhanced Enchantment Management:
- During extraction, other enchantments on the item are now preserved.
- Use of {_target}.clone() for better preview of enchantment application results.

3. XP Cost Integration in Interface:
- XP cost now displayed in the anvil interface (anvil repair cost).
- Player's XP level check before allowing the operation.

4. Improved User Messages:
- Display of XP cost for each successful operation.
- Error message if the player doesn't have enough XP.

5. Better Handling of Special Cases:
- Book quantity check during extraction (must be 1).
- Added condition to let vanilla behavior handle non-specific cases.

6. Code Optimization and Clarification:
- Code restructuring for better readability and maintenance.
- Comments added to explain different process steps.

This update brings a more balanced and vanilla-like system for enchantment management. The new XP cost system adds a strategic dimension to enchantment usage, while preserving the flexibility offered by custom enchantment extraction and application.

Enjoy these new features for an enriched and more balanced gameplay experience!

Feel free to share your feedback and suggestions to continue improving this script.