Amethyst buds aren't marked as non-pathfindable

Amethyst bud blocks have a non-full block shape, but are not marked as non-pathfindable; the block doesn't override the isPathfindable() method to return false, like other blocks do (e.g. the hopper, or bamboo).

This causes entities to get stuck on them, since they will try to pathfind through instead of going around them.