feat(game): 动物自然生成（草面/白天/限频）与繁殖冷却/成长；村民交易表数据驱动（含测试）

assets/config/villager_trades.json

@@ -0,0 +1,20 @@
+{
+  "professions": {
+    "farmer": [
+      { "buy": "wheat", "buy_n": 20, "sell": "rotten_flesh", "sell_n": 1 },
+      { "buy": "wheat", "buy_n": 3, "sell": "beef", "sell_n": 1 }
+    ],
+    "builder": [
+      { "buy": "oak_planks", "buy_n": 16, "sell": "stick", "sell_n": 4 },
+      { "buy": "cobblestone", "buy_n": 8, "sell": "oak_planks", "sell_n": 4 }
+    ],
+    "blacksmith": [
+      { "buy": "coal", "buy_n": 8, "sell": "iron_ingot", "sell_n": 1 },
+      { "buy": "iron_ingot", "buy_n": 2, "sell": "diamond", "sell_n": 1 }
+    ],
+    "trader": [
+      { "buy": "rotten_flesh", "buy_n": 8, "sell": "bone", "sell_n": 2 },
+      { "buy": "feather", "buy_n": 4, "sell": "egg", "sell_n": 1 }
+    ]
+  }
+}