Function ternary_gemm_cpu_2bit 

pub fn ternary_gemm_cpu_2bit(
    activations: &[f32],
    packed: &[u8],
    scale: f32,
    n_in: usize,
    n_out: usize,
    n_batch: usize,
    in_row_stride: usize,
    out_row_stride: usize,
    out: &mut [f32],
)

CPU oracle for ternary_gemm_2bit.wgsl — same math as ternary_gemm_cpu, 2-bit packing + branchless accumulation.