根本问题：缓存键名不匹配
LoadNpcSprites 时:
mapping = {enemyType → npcName} (如 "bread_loaf" → "淀粉酶NPC")
cacheNpcPixels("bread_loaf", ...) ← 以 enemyType 为 key 缓存
DrawEnzymeNpc 时:
Render.GetSpriteData(npc.typeNam