Function cross_reference 

pub fn cross_reference(
    duplication: &DuplicationReport,
    dead_code: &AnalysisResults,
) -> CrossReferenceResult

Cross-reference duplication findings with dead code analysis results.

For each clone instance, checks whether:

1. The file is entirely unused (in unused_files)
2. An unused export/type at the same line range overlaps

Returns combined findings sorted by priority (unused files first, then exports).