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/fsspec/implementations/chained.py

@@ -0,0 +1,23 @@
+from typing import ClassVar
+
+from fsspec import AbstractFileSystem
+
+__all__ = ("ChainedFileSystem",)
+
+
+class ChainedFileSystem(AbstractFileSystem):
+    """Chained filesystem base class.
+
+    A chained filesystem is designed to be layered over another FS.
+    This is useful to implement things like caching.
+
+    This base class does very little on its own, but is used as a marker
+    that the class is designed for chaining.
+
+    Right now this is only used in `url_to_fs` to provide the path argument
+    (`fo`) to the chained filesystem from the underlying filesystem.
+
+    Additional functionality may be added in the future.
+    """
+
+    protocol: ClassVar[str] = "chained"