Call-graph reference: Rust (rust-analyzer SCIP)

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Part of #3772. Follows the SCIP evaluation: if SCIP is adopted, this is its adapter, run over rust-analyzer scip.

• Corpus: serde-rs/json, pinned in tests/import_graph_corpus.json.
• Adapter: map impl blocks, trait methods and Type::method to the engine's naming.
• Expected findings:
  • trait method declarations without a default body, which are bodyless (Call resolver (TypeScript): confident links land on bodyless signatures (interface / abstract / type members) instead of the code that runs #3757's pattern);
  • macro-generated calls (serde derives), which no text-based extractor can see. Label that a deliberate limit, not a defect.