Potion Packs - Custom Potions

Fix potion family resolution and add deep loader diagnostics

- Fixed external folder potion packs resolving zero variants despite valid effect ids
- Reworked deferred MobEffect registry lookup flow to resolve effects only after Forge registries are fully available
- Fixed potion family validation incorrectly discarding valid vanilla effects
- Added explicit variant generation diagnostics for:
  - normal potions
  - strong potions
  - long potions
  - splash combinations
  - lingering combinations
- Added logs for:
  - external pack discovery
  - archive pack discovery
  - namespace resolution
  - parsed family counts
  - override merge operations
  - disable rule application
  - brewing recipe generation
  - deferred registration execution
  - final registered potion totals
- Improved error reporting for malformed potion definitions
- Added effect registry existence checks with detailed namespace/id output
- Fixed parsing edge cases with brewing recipe structures
- Fixed external folder pack traversal not entering nested potionpacks directories correctly
- Fixed family resolution pipeline producing empty enabled variant sets
- Improved merge behavior for partial overrides so only explicitly defined values replace originals
- Added safer fallback handling for missing tiers, durations, and brewing combinations
- Added more verbose warnings for skipped families and disabled variants
- Cleaned up loader initialization ordering and startup diagnostics
- Improved compatibility foundations for addon-provided internal potion packs