perf(nav): reduce code-rank path and membership overhead

[ClaudiuCeia]

Finding

Code-rank repeatedly performs target membership checks and canonical path work during a single ranking run. These operations are safe to cache per run and can become significant on larger TypeScript projects.

Proposed approach

• Replace repeated target-array membership checks with a Set in packages/nav/src/service.ts.
• Cache canonicalized paths for the duration of one rank operation in packages/nav/src/code-rank/rank.ts.
• Add a representative code-rank benchmark and focused correctness coverage for path aliases/canonicalization.
• Keep the optimization scoped to a single run. Do not persist or reuse the language service while scripts use a fixed version of "0", because that would permit stale program state.

Acceptance criteria

• Ranking output and tie behavior remain unchanged.
• Target membership is constant-time after setup.
• Each distinct path is canonicalized at most once per ranking run.
• Symlink/case-normalization behavior remains correct on supported platforms.
• A benchmark demonstrates the effect on a multi-file fixture.
• Full nav and workspace validation passes.