Function cross_pairs 

pub fn cross_pairs(
    first: &[[f32; 3]],
    second: &[[f32; 3]],
    cutoff: f32,
    backend: SpatialBackend,
    context: &ExecutionContext,
) -> Result<Vec<CrossPair>, SpatialError>

Find cross-set neighbours without producing within-set pairs.

The coordinate workspace respects the shared execution memory budget. Output order follows the first index and then the second index deterministically.

Errors

Returns an error for invalid coordinates or cutoff, overflowing indices, cancellation, or insufficient execution memory.