Restrict leaf litter to the dappled Forest

Leaf litter should only spawn naturally in the Dappled Forest biome to balance building mechanics, reduce early-game inventory clutter, and preserve the distinct identity of classic biomes. While leaf litter is a fantastic decorative feature, its widespread appearance in standard forests can disrupt the vibrant, traditional green aesthetic that many players prefer for their classic builds. Restricting its natural world generation to the Dappled Forest would instantly give that specific biome a much stronger, exclusive autumnal identity tied to its unique poplar trees and orange-brown turf. Furthermore, because leaf litter is already easily renewable and farmable by burning regular leaves in the furnace, builders would still have full access to this decorative block anywhere they want without impacting the natural world generation of other biomes.