io_storages/filesystem.py is a dead module — its `from .base import …` target doesn't exist

Describe the bug label_studio/io_storages/filesystem.py:10 does from .base import BaseForm, BaseStorage, CloudStorage, but no base module exists in io_storages/ (nearest is base_models.py, which does not define BaseForm or CloudStorage). Importing the module raises ModuleNotFoundError immediately.

A repo-wide search finds zero importers of this module, so nothing currently breaks — but it's a landmine: the first future import crashes. Suggest either deleting the file or fixing the import if it's meant to be live; happy to PR whichever you prefer.

To Reproduce

1. python -c "import label_studio.io_storages.filesystem" → ModuleNotFoundError: No module named 'label_studio.io_storages.base'
2. ls label_studio/io_storages/ → no base.py
3. grep -rn "io_storages.filesystem\|from .filesystem\|import filesystem" label_studio/ → zero importers

Expected behavior Modules in the package either import cleanly or don't ship.

Screenshots n/a

Environment (please complete the following information):

• OS: n/a (code-level finding)
• Label Studio Version: develop @ 63fdee07510d873e39920b1f75daedae721e71ca (2026-07-12)

Additional context Found while validating DACIP, a static contract-analysis tool I'm building, against open-source codebases.