[Story][FEA] Grouped range-window support in cuDF-Polars

[rjzamora]

This story tracks grouped range-window features in cudf-polars. These features all involve window bounds defined by an index/order column within each group.

Action Items:

• Dynamic groupby ([FEA] Support for dynamic groupby in cudf-polars #17144)
• Grouped LazyFrame.rolling ([FEA] Support grouped LazyFrame.rolling in cuDF-Polars #23590)
• Grouped rolling via over
  • First pass: Small-group support ([Story][FEA] Complete grouped over expression coverage in cuDF-Polars #23606)
  • Second pass: Large group support (TBD)