Function find_dominated_rules 

pub fn find_dominated_rules(
    graph: &ReductionGraph,
) -> (Vec<DominatedRule>, Vec<UnknownComparison>)

Find all primitive reduction rules dominated by composite paths.

Returns a tuple of:

• Vec<DominatedRule>: rules proven dominated by a composite path
• Vec<UnknownComparison>: candidates that could not be decided

For each primitive rule (direct edge), enumerates all alternative paths, validates trustworthiness, composes overheads, and compares. Keeps only the best (shortest) dominating path per primitive rule.

Note: iterates the graph’s coalesced edges rather than raw inventory entries. This is sound because test_no_duplicate_primitive_rules_per_variant_pair guards the invariant that at most one registration exists per (source_variant, target_variant) pair.