Function conditional_copy_i32_to 

pub fn conditional_copy_i32_to(
    mask: &BooleanArray<()>,
    then_data: &[i32],
    else_data: &[i32],
    output: &mut [i32],
)

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.