Function bgemm_raw_with_backend_into 

pub fn bgemm_raw_with_backend_into<T, B>(
    c: RawStridedMut<'_, T>,
    a: RawStridedRef<'_, T>,
    b: RawStridedRef<'_, T>,
    n_batch: usize,
    n_lo: usize,
    n_ro: usize,
    n_sum: usize,
    alpha: T,
    beta: T,
    conj_a: bool,
    conj_b: bool,
) -> Result<(), EinsumError>
where
    T: ScalarBase + ElementOpApply,
    B: Backend<T>,

Batched strided GEMM on raw borrowed metadata using an explicit backend.

Backend implementations that do not provide a specialized raw path use the same preparation pipeline as einsum2_dispatch: materialize/copy only when the backend requires it, call Backend::bgemm_contiguous_into, then finalize the destination.