Implement .collect() as alias for .clone() for DataFrame

[erikamundson]

Description

It would be convenient to allow calls to .collect() on a DataFrame to return a copy (same behavior as .clone()).

Currently LazyFrame allows .lazy() which allows us to write a function that accepts either a LazyFrame or a materialized DataFrame and returns a Lazy copy of that object.

def ensure_lazy(frame: DataFrame | LazyFrame) -> LazyFrame:
    return frame.lazy()

It would be useful to also be able to write a similar function that always returns a materialized DataFrame.

def ensure_materialized(frame: DataFrame | LazyFrame) -> DataFrame:
    return frame.collect()

We can get around it right now by calling frame.lazy().collect() but there may be additional overhead to converting from DataFrame to Lazy and back again, rather than just cloning the DataFrame directly.

Happy to give this a go myself if approved.

[Wainberg]

I mean, if lf.lazy() is a lazyframe, then df.collect() should be a dataframe.

[MarcoGorelli]

I think this was discussed and rejected, could you search the issue tracker please?

EDIT: here it is #7882 (comment)

[erikamundson]

Ah sorry @MarcoGorelli I missed that when searching. Will close this one.