[FEA] Support for dynamic groupby in cudf-polars

[wence-]

Is your feature request related to a problem? Please describe.

Polars supports group_by_dynamic that does (approximately) grouped rolling windows.

We do not currently support this in cudf-polars, what is more, the IR doesn't distinguish between normal groupbys and dynamic groupbys when we get it from polars. Consequently, we only fall back to CPU based on some heuristics, and sometimes just do the wrong thing.

Describe the solution you'd like

• Expose dynamic groupbys in the IR (refactor(python): Expose group_by_dynamic in pyir pola-rs/polars#19385, in polars 1.11)
• Raise that they're not implemented (Upgrade to polars 1.11 in cudf-polars #17154, in cudf nightlies)
• Implement them.

[wence-]

Exposure, so we at least can fall back correctly in polars is pola-rs/polars#19385

[vyasr]

@wence- is there urgency to get this actually implemented, or are we OK with fallback for 24.12 (now that pola-rs/polars#19385 is out) while we work on higher priority tasks like inequality joins?

[wence-]

I think the implementation can wait a bit. I think it falls under the aegis of rolling window stuff, so needs work related to that too.