Teal Lib

• Thread the WorldGenRegion accessor through variant assignment so biome, height and weather lookups stay region-local and non-blocking. They previously routed through the entity's ServerLevel and could block a worldgen worker on an off-thread chunk load, deadlocking chunk generation.
• Select the weighted variant with a fresh per-call RandomSource. The shared level RNG is not thread-safe under parallel chunk generation and tripped the ThreadingDetector. This also removes the need for the c2me special case.
• Defer variant assignment to the first entity tick when the spawn chunk is not yet queryable, covering structure-placed spawns.
• Pass the accessor into applyEntity so variant data implementations can query the level.

Thanks nacolla!