Function rs_code_matrix 

pub fn rs_code_matrix(
    log_blowup: usize,
    layout: &StackedLayout,
    traces: &[&DeviceMatrix<F>],
    stacked_matrix: &Option<PleMatrix<F>>,
    device_ctx: &GpuDeviceCtx,
) -> Result<DeviceMatrix<F>, RsCodeMatrixError>

Computes the Reed-Solomon codeword of each column vector of eval_matrix where the rate is 2^{-log_blowup}. The column vectors are treated as evaluations of a prismalinear extension on a hyperprism.

Uses stacked_matrix if available, or else stacks traces directly into final codeword matrix buffer.