feat: add Lootr mod integration for Treasure Chests

[Dangocan]

Summary

• Adds compatibility with Lootr mod to provide per-player loot generation for Treasure Chests
• When Lootr is installed, each player gets their own unique inventory when opening a Treasure Chest
• Implements ILootrBlockEntityConverter service for seamless integration with Lootr's API

Changes

• build.gradle / gradle.properties: Added Lootr Maven dependency for full API access
• TreasureChestBlock: Added Lootr integration hooks for opening chests and handling destruction
• TreasureChestBlockEntity: Added Lootr-specific fields and methods for tracking per-player state
• AetherAtlases / TreasureChestRenderer: Added support for Lootr's opened/unopened chest textures
• New integration package: LootrCompat, LootrTreasureChestInfoProvider, TreasureChestBlockEntityConverter

Test plan

• Verify Treasure Chests work normally without Lootr installed
• Install Lootr and verify per-player loot generation works
• Test chest opening/closing animations with Lootr
• Verify chest destruction properly notifies Lootr
• Test shift-click behavior for Lootr info display