Function conditional_copy_u32_to 

pub fn conditional_copy_u32_to(
    mask: &BooleanArray<()>,
    then_data: &[u32],
    else_data: &[u32],
    output: &mut [u32],
)

Zero-allocation variant: writes directly to caller’s output buffer.

Conditional copy operation: select elements from then_data or else_data based on boolean mask. Panics if output.len() != mask.len.