Rust precision: short-name Unknown widening explodes on dense crates #20

Real-world run on ogulcancelik/herdr (single dense crate, 3085 tests, 62k call refs, 41k unresolved): every commit selects 722-2949 tests. Tier-1's Unknown-by-short-name widening plus a highly connected module graph sweeps most of the crate on any change. Candidates: qualifier-aware Unknown matching, per-crate name scoping, SCIP tier 2. Repro: clone herdr, testless index, testless select --from HEAD^ on recent commits.