Function prepare_output_raw 

pub fn prepare_output_raw<T>(
    view: &mut RawStridedMut<'_, T>,
    n_group1: usize,
    n_group2: usize,
    beta: T,
    requires_unit_stride: bool,
    use_pool: bool,
) -> Result<ContiguousOperandMut<T>, EinsumError>
where
    T: ScalarBase + 'static,

Prepare a borrowed raw output layout for GEMM.

This is the raw-layout counterpart to prepare_output_view. Direct fusable layouts do not construct StridedViewMut wrappers; a view is created only when a copy/writeback path needs a generic strided kernel.