Store `started_at` or duration info in cached steps too
This would help to better monitor how much time a step take, especially depending on dataset size, so that we can see how certain changes influence processing speed and make more informed decisions about these changes and our size limits (see https://github.com/huggingface/dataset-viewer/issues/2878). Especially useful for duckdb and statistics step.

I can work on this if you think it's useful (I think it is) and don't break any logic.
Store `started_at` or duration info in cached steps too: This would help to better monitor how much time a step take, especially depending on dataset size, so that we can see how certain changes influence processing speed and make more informed decisions about these changes and our size limits (see https://github.com/huggingface/dataset-viewer/issues/2878). Especially useful for duckdb and statistics step.

I can work on this if you think it's useful (I think it is) and don't break any logic.