[FEA] Pass `keys_are_sorted` in intermediate groupby operation in cudf_polars

(Identified by Claude)

Similar to what was already done in regular groupby operations. If the input column is sorted, `keys_are_sorted=plc.types.Sorted.YES` should be passed into intermediate groupby operations like:

https://github.com/rapidsai/cudf/blob/01c7adae10d12da7a175fb616300f8190522b6e0/python/cudf_polars/cudf_polars/dsl/expressions/unary.py#L283-L284

And if applicable like what was done in https://github.com/rapidsai/cudf/pull/21871, mark resulting resulting columns of the groupby keys as sorted like in

https://github.com/rapidsai/cudf/blob/01c7adae10d12da7a175fb616300f8190522b6e0/python/cudf_polars/cudf_polars/dsl/expressions/rolling.py#L744

https://github.com/rapidsai/cudf/blob/01c7adae10d12da7a175fb616300f8190522b6e0/python/cudf_polars/cudf_polars/dsl/expressions/rolling.py#L291