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/util.py

@@ -0,0 +1,47 @@
+# Copyright 2017 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.
+
+from . import encode
+from . import number_types
+from . import packer
+
+
+def GetSizePrefix(buf, offset):
+  """Extract the size prefix from a buffer."""
+  return encode.Get(packer.int32, buf, offset)
+
+
+def GetBufferIdentifier(buf, offset, size_prefixed=False):
+  """Extract the file_identifier from a buffer"""
+  if size_prefixed:
+    # increase offset by size of UOffsetTFlags
+    offset += number_types.UOffsetTFlags.bytewidth
+  # increase offset by size of root table pointer
+  offset += number_types.UOffsetTFlags.bytewidth
+  # end of FILE_IDENTIFIER
+  end = offset + encode.FILE_IDENTIFIER_LENGTH
+  return buf[offset:end]
+
+
+def BufferHasIdentifier(buf, offset, file_identifier, size_prefixed=False):
+  got = GetBufferIdentifier(buf, offset, size_prefixed=size_prefixed)
+  return got == file_identifier
+
+
+def RemoveSizePrefix(buf, offset):
+  """Create a slice of a size-prefixed buffer that has
+
+  its position advanced just past the size prefix.
+  """
+  return buf, offset + number_types.Int32Flags.bytewidth