Legendary Gemstones

### New
- Mossy box loot is now configurable via datapack,

### Changes
- Split mixin classes from common module into per-platform source sets,
- Gemstone socket components now use lazy initialization, preventing premature registry access on NeoForge,
- Removed particle effects from area damage modifiers to reduce visual noise,
- Reworked attributes and effects registry initialization to use RegistrySupplier directly instead of eager resolveEntry(), preventing NullPointerException on NeoForge startup,

### Fixes
- Fixed duplicate blockDrops merge check in DropsConfig,
- Fixed crash on NeoForge caused by mixin refmap containing Yarn intermediary class names instead of Mojang-mapped names,
- Fixed crash on NeoForge: "Registry Object not present: gemstones:pull_speed" and similar attribute registry failures,
- Fixed effects registry crash on NeoForge during mod construction,
- Fixed Onyx and Ender Scale bonuses causing game crash due to null registry references,
- Fixed Fabric registries failing after refactor,