JEI Structures(EMI/JEI)

English:
Added persistent natural-spawn markers and filtered naturally spawned mobs from structure capture. Added automatic structure index export when the cache is missing, empty, or invalid.

中文：
新增自然生成生物持久化标记，结构采集跳过自然生成生物；结构索引缓存缺失、为空或损坏时，服务器启动后自动导出。