Added the item collection and search

Included in this release:

• Collection: Cleaned up interfaces to handle global and mod item collections.
• Items: Introduced the global item collection.
• Items: Added getTags() and getAuthors(), inherited from the mod.
• Items: Added item filtering capabilities.
• Items: Added getCETCommand().
• Items: Added getCETCommands() to the mod item collection.
• Filters: Added filtering by author.
• Core: Refactored for a cleaner class structure.
• Core: PHPStan clean @ level 9.