feat(资源): 添加钻石巧克力和猫头鹰角色资源

新增钻石巧克力(Diamond.tscn)和猫头鹰(MTY.tscn)角色资源及相关图片文件
调整猫和狗的掉落物品数量范围
修改EntityBase.gd中物品掉落数量的计算逻辑

resources/characters/bird/mty.png.import

@@ -0,0 +1,40 @@
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+"vram_texture": false
+}
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+[deps]
+
+source_file="res://resources/characters/bird/mty.png"
+dest_files=["res://.godot/imported/mty.png-35e99f5b820fd3ecfd8432b4a6f28277.ctex"]
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+compress/normal_map=0
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+mipmaps/generate=false
+mipmaps/limit=-1
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+process/channel_remap/blue=2
+process/channel_remap/alpha=3
+process/fix_alpha_border=true
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+process/normal_map_invert_y=false
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+process/size_limit=0
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