Function classify_for_parallel_execution 

pub fn classify_for_parallel_execution(
    specs: &[MutationSpec],
) -> (Vec<Vec<usize>>, Vec<usize>)

Classify specs into parallelizable groups (DEPRECATED).

This function is deprecated and will be removed. Use conflict::group_by_conflicts directly. The old logic depended on item_refs() which doesn’t work with lazy MutationTargetSymbol.

For now, this function simply calls group_by_conflicts for all specs.