fix(arborist): avoid repeated peer placement checks

[drewmt]

Summary

Dense cyclic peer graphs can reach the same placement state through many different paths. The existing peerPath guard prevents direct recursion, but still repeats equivalent checks and can leave npm install CPU-bound indefinitely.

This keeps a traversal-scoped record of peer checks keyed by the peer edge, placement target, and deepest target. Distinct placement contexts are still evaluated, while duplicate paths are skipped.

The reported install now completes successfully with 454 packages instead of remaining CPU-bound.

Fixes #9934

Testing

• Full @npmcli/arborist test suite
• npm run eslint -w @npmcli/arborist
• npm install @deepseek-ai/dsh@0.1.1-rc.2 --package-lock-only --ignore-scripts on Node 24.15.0 and npm 12.0.2