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/flatbuffers/packer.py

@@ -0,0 +1,41 @@
+# Copyright 2016 Google Inc. All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Provide pre-compiled struct packers for encoding and decoding.
+
+See: https://docs.python.org/2/library/struct.html#format-characters
+"""
+
+import struct
+from . import compat
+
+
+boolean = struct.Struct(compat.struct_bool_decl)
+
+uint8 = struct.Struct("<B")
+uint16 = struct.Struct("<H")
+uint32 = struct.Struct("<I")
+uint64 = struct.Struct("<Q")
+
+int8 = struct.Struct("<b")
+int16 = struct.Struct("<h")
+int32 = struct.Struct("<i")
+int64 = struct.Struct("<q")
+
+float32 = struct.Struct("<f")
+float64 = struct.Struct("<d")
+
+uoffset = uint32
+soffset = int32
+voffset = uint16