Support dask_expr migration into dask.dataframe

[rjzamora]

Description

Follow up to #17558
This PR cleans up some imports and provides support for both dask:2024.12.1 and dask:main (in which dask_expr has been moved into the dask.dataframe module).

See also: rapidsai/dask-cuda#1424

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

[madsbk]

Looks good. I guess, we expect the dask>2024.12.1 pinning fairly soon right? Otherwise, we might consider moving all of the dask_expr imports to a centralized place.

[rjzamora]

I guess, we expect the dask>2024.12.1 pinning fairly soon right?|

I think we will either stay pinned to dask:2024.12.1 for rapids:25.02 (but continue efforts like this to stay as aligned with dask:main as possible), or we will end up pinning to 2025.1.<something> in the next two weeks.

Otherwise, we might consider moving all of the dask_expr imports to a centralized place.

Yeah, totally agree. I actually tried this initially, but I struggled to find a structure I was happy with. That said, I could be missing an obvious design pattern that would have made everything cleaner.

[madsbk]

Yeah, totally agree. I actually tried this initially, but I struggled to find a structure I was happy with. That said, I could be missing an obvious design pattern that would have made everything cleaner.

I think it is fine as is

[pentschev]

Changes mostly make sense to me except for the message to downgrade for which I left a comment. WDYT @rjzamora ?