Fix off-by-one num_segments in matrix::sort_cols_per_row

[viclafargue]

Closes #2049

raft::matrix::detail::sortColumnsPerRow passed n_rows + 1 to cub as num_segments. Per the cub contract, an aliased CSR offsets array must have length num_segments + 1, so cub read one int past the offsets allocation. This crashes with cudaErrorIllegalAddress when n_rows + 1 is a power of two ≥ 64 and n_columns ≥ ~16384 (silent otherwise).

Surfaces in cuvs::stats::trustworthiness_score whenever n % batch_size ∈ {63, 127, 255, …} (e.g. n=76927, batch_size=512).

Fix : pass n_rows to cub; size the offsets array as n_rows + 1.