Reproduce discarded safe-layer DRC improvement

[ShiboSoftwareDev]

Issue

The safe trace-layer phase can reduce the exact DRC count, but the portfolio discards the candidate unless it removes every trace and pad error.

Reproduction

The snapshot shows the failure directly: the input has 4 DRC errors, the safe-layer candidate has 1, and the portfolio still returns the 4-error input.

This PR contains only the focused test and its SVG snapshot.

Checks

• bun test tests/safe-trace-layer-move.test.ts
• bun run formatcheck
• bun run typecheck

[tscircuitbot]

Benchmark This PR

Run benchmarks by commenting on this PR:

/benchmark [benchmark.sh args...]
/benchmark [scenario-limit|all] --dataset <drc14|srj18> --concurrency <n> --effort <n> --max-iterations <n>

Everything after /benchmark is forwarded directly to ./benchmark.sh.

Examples:

• /benchmark -> run default SRJ18 benchmark settings
• /benchmark 10 -> run first 10 SRJ18 samples
• /benchmark --dataset srj18 -> run all SRJ18 samples
• /benchmark 1 --dataset srj18 -> run the first SRJ18 sample
• /benchmark --dataset drc14 -> run all DRC14 samples
• /benchmark all --concurrency 4 -> run all SRJ18 samples with 4 workers
• /benchmark --scenario-limit all --effort 2 -> run all samples with effort 2
• /benchmark --scenario-limit 20 --max-iterations 100 -> run 20 samples with a max iteration override

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