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/backend/mixins.py

@@ -0,0 +1,76 @@
+"""Mixin classes used by Base subclasses to inherit backend functionality."""
+
+import os
+import typing
+
+from .. import parameters
+
+from . import piping
+from . import rendering
+from . import unflattening
+from . import viewing
+
+__all__ = ['Render', 'Pipe', 'Unflatten', 'View']
+
+
+class Render(parameters.Parameters):
+    """Parameters for calling and calling ``graphviz.render()``."""
+
+    def _get_render_parameters(self,
+                               outfile: typing.Union[os.PathLike, str, None] = None,
+                               raise_if_result_exists: bool = False,
+                               overwrite_source: bool = False,
+                               **kwargs):
+        kwargs = self._get_parameters(**kwargs)
+        kwargs.update(outfile=outfile,
+                      raise_if_result_exists=raise_if_result_exists,
+                      overwrite_filepath=overwrite_source)
+        return [kwargs.pop('engine'), kwargs.pop('format')], kwargs
+
+    @property
+    def _render(_):  # noqa: N805
+        """Simplify ``._render()`` mocking."""
+        return rendering.render
+
+
+class Pipe(parameters.Parameters):
+    """Parameters for calling and calling ``graphviz.pipe()``."""
+
+    _get_format = staticmethod(rendering.get_format)
+
+    _get_filepath = staticmethod(rendering.get_filepath)
+
+    def _get_pipe_parameters(self, **kwargs):
+        kwargs = self._get_parameters(**kwargs)
+        return [kwargs.pop('engine'), kwargs.pop('format')], kwargs
+
+    @property
+    def _pipe_lines(_):  # noqa: N805
+        """Simplify ``._pipe_lines()`` mocking."""
+        return piping.pipe_lines
+
+    @property
+    def _pipe_lines_string(_):  # noqa: N805
+        """Simplify ``._pipe_lines_string()`` mocking."""
+        return piping.pipe_lines_string
+
+
+class Unflatten:
+
+    @property
+    def _unflatten(_):  # noqa: N805
+        """Simplify ``._unflatten mocking."""
+        return unflattening.unflatten
+
+
+class View:
+    """Open filepath with its default viewing application
+        (platform-specific)."""
+
+    _view_darwin = staticmethod(viewing.view_darwin)
+
+    _view_freebsd = staticmethod(viewing.view_unixoid)
+
+    _view_linux = staticmethod(viewing.view_unixoid)
+
+    _view_windows = staticmethod(viewing.view_windows)