fix duckdb circular import
When deploying to staging (and also locally), the following error appeared for /search service:
![Screenshot from 2023-10-27 12-34-59](https://github.com/huggingface/datasets-server/assets/5564745/78784b8f-94f8-41fa-8a7e-6a473bb35f2c)

fix duckdb circular import: When deploying to staging (and also locally), the following error appeared for /search service:
![Screenshot from 2023-10-27 12-34-59](https://github.com/huggingface/datasets-server/assets/5564745/78784b8f-94f8-41fa-8a7e-6a473bb35f2c)
