New Deer update

Introduce a new interactive mob: deer, which can be ridden by players and naturally spawns in forest biomes in groups. Deer antlers can be customized with decorations such as wreaths, bells, or ornaments, and the antlers can also function as a musical instrument or flute. When players play the antler flute, nearby deer are attracted to the sound and follow the player, approaching using natural AI behavior, either walking calmly or trotting. Riding deer grants players slightly faster movement and higher jumps, and deer that follow the player via the flute will stay nearby for a limited time, providing companionship and enhancing exploration. Deer behavior is dynamic, including grazing, wandering, and interacting with other mobs, and all animations should be smooth and natural. The flute sound should be gentle and melodic, making the experience immersive, and players can optionally decorate the deer for festive events or customize their appearance with different antler types and patterns.