chore: 添加虚拟环境到仓库

- 添加 backend_service/venv 虚拟环境
- 包含所有Python依赖包
- 注意：虚拟环境约393MB，包含12655个文件

backend_service/venv/lib/python3.13/site-packages/socketio/msgpack_packet.py

@@ -0,0 +1,18 @@
+import msgpack
+from . import packet
+
+
+class MsgPackPacket(packet.Packet):
+    uses_binary_events = False
+
+    def encode(self):
+        """Encode the packet for transmission."""
+        return msgpack.dumps(self._to_dict())
+
+    def decode(self, encoded_packet):
+        """Decode a transmitted package."""
+        decoded = msgpack.loads(encoded_packet)
+        self.packet_type = decoded['type']
+        self.data = decoded.get('data')
+        self.id = decoded.get('id')
+        self.namespace = decoded['nsp']