Function group_pairs 

pub fn group_pairs(
    pairs: &[ClonePair],
    files: &[InputFile<'_>],
    config: &EngineConfig,
) -> Vec<CloneGroup>

Group clone pairs into clone groups by matched content.

Instances are deduplicated across pairs, members are sorted, and the canonical instance is the first member under (file, token range) order. Groups come back sorted by their canonical instance, so output order does not depend on input order.