Fix parent XO config resolution from nested package cwd

[sjh9714]

Summary

Fixes XO config resolution when running from a nested package in a monorepo.

What changed

• Added regression coverage for resolving a parent package.json XO config from a nested package cwd.
• Updated config discovery to search parent project directories instead of stopping at the package parent directory.

Why

Issue #733 reports that packages in a monorepo do not pick up the root XO config. The previous search stopped before reaching the monorepo root.

Testing

• npm run build
• npm run test:setup
• npx ava dist/test/resolve-config.test.js
• node dist/cli.js lib/resolve-config.ts test/resolve-config.test.ts
• git diff --check

Note: I also checked npm test; it currently stops at the lint step on both this branch and upstream/main with the same pre-existing @typescript-eslint/no-unnecessary-type-assertion reports in lib/utils.ts and lib/xo.ts.

Fixes #733