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/parameters/mixins.py

@@ -0,0 +1,46 @@
+"""Mixin classes used to inherit parameter functionality."""
+
+import typing
+
+from . import engines
+from . import formats
+from . import renderers
+from . import formatters
+
+__all__ = ['Parameters']
+
+
+class Parameters(engines.Engine, formats.Format,
+                 renderers.Renderer, formatters.Formatter):
+    """Parameters for calling ``graphviz.render()`` and ``graphviz.pipe()``."""
+
+    def _get_parameters(self, *,
+                        engine: typing.Optional[str] = None,
+                        format: typing.Optional[str] = None,
+                        renderer: typing.Optional[str] = None,
+                        formatter: typing.Optional[str] = None,
+                        verify: bool = False,
+                        **kwargs):
+        if engine is None:
+            engine = self.engine
+        elif verify:
+            self._verify_engine(engine)
+
+        if format is None:
+            format = self.format
+        elif verify:
+            self._verify_format(format)
+
+        if renderer is None:
+            renderer = self.renderer
+        elif verify:
+            self._verify_renderer(renderer)
+
+        if formatter is None:
+            formatter = self.formatter
+        elif verify:
+            self._verify_formatter(formatter)
+
+        kwargs.update(engine=engine, format=format,
+                      renderer=renderer, formatter=formatter)
+        return kwargs