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/graphviz/saving.py

@@ -0,0 +1,83 @@
+"""Save DOT source lines to a file."""
+
+import logging
+import os
+import typing
+
+from . import _defaults
+from . import _tools
+from . import base
+from . import encoding
+
+__all__ = ['Save']
+
+log = logging.getLogger(__name__)
+
+
+class Save(encoding.Encoding, base.Base):
+    """Save DOT source lines to file."""
+
+    directory: typing.Union[str, bytes] = ''
+
+    _default_extension = _defaults.DEFAULT_SOURCE_EXTENSION
+
+    _mkdirs = staticmethod(_tools.mkdirs)
+
+    def __init__(self, *,
+                 filename: typing.Union[os.PathLike, str],
+                 directory: typing.Union[os.PathLike, str, None] = None,
+                 **kwargs) -> None:
+        super().__init__(**kwargs)
+
+        if filename is None:
+            filename = f'{self.__class__.__name__}.{self._default_extension}'
+
+        self.filename = os.fspath(filename)
+        """str: Target file name for saving the DOT source file."""
+
+        if directory is not None:
+            self.directory = os.fspath(directory)
+
+    def _copy_kwargs(self, **kwargs):
+        """Return the kwargs to create a copy of the instance."""
+        assert 'directory' not in kwargs
+        if 'directory' in self.__dict__:
+            kwargs['directory'] = self.directory
+        return super()._copy_kwargs(filename=self.filename, **kwargs)
+
+    @property
+    def filepath(self) -> str:
+        """The target path for saving the DOT source file."""
+        return os.path.join(self.directory, self.filename)
+
+    @_tools.deprecate_positional_args(supported_number=1, ignore_arg='self')
+    def save(self, filename: typing.Union[os.PathLike, str, None] = None,
+             directory: typing.Union[os.PathLike, str, None] = None, *,
+             skip_existing: typing.Optional[bool] = False) -> str:
+        """Save the DOT source to file. Ensure the file ends with a newline.
+
+        Args:
+            filename: Filename for saving the source (defaults to ``name`` + ``'.gv'``)
+            directory: (Sub)directory for source saving and rendering.
+            skip_existing: Skip write if file exists (default: ``False``).
+
+        Returns:
+            The (possibly relative) path of the saved source file.
+        """
+        if filename is not None:
+            self.filename = filename
+        if directory is not None:
+            self.directory = directory
+
+        filepath = self.filepath
+        if skip_existing and os.path.exists(filepath):
+            return filepath
+
+        self._mkdirs(filepath)
+
+        log.debug('write lines to %r', filepath)
+        with open(filepath, 'w', encoding=self.encoding) as fd:
+            for uline in self:
+                fd.write(uline)
+
+        return filepath