Fix oxlint plugin test on Windows

[snowyukitty]

What does this change?

Fixes #220.

Convert the absolute path returned by require.resolve() to a file: URL before dynamically importing Vite+'s pinned oxlint plugin test helper. This lets the test file start on Windows, where a raw drive-letter path is not a valid ESM specifier.

Why is this obviously correct and trivially verifiable?

pathToFileURL() is Node's standard conversion from a filesystem path to an importable file URL. The resolved module and all test behavior remain unchanged; only the representation passed to import() changes. The patch adds one standard-library import and wraps the existing resolved path.

Verification on Windows with Node 22.22.3 and pnpm 11.17.0:

• node --test scripts/oxlint-plugin.test.js — 32 passed
• pnpm lint:check — passed (existing warnings only)
• pnpm lint — lint passed, but the recursive type/build phase hit the existing spawnSync pnpm ENOENT failure in unchanged packages/gatekeeper-scheduler/build-app.mjs tracked by pnpm run-local cannot start on Windows: spawnSync pnpm ENOENT #19 and fix: invoke pnpm via npm_execpath on Windows (fixes #19) #107

AI tools assisted the investigation, patch drafting, and review. The failure and verification results above were reproduced locally.

Checklist

• This is a small, concrete change; it is not a feature, refactor, or low-value cleanup.
• I understand that maintainers decide whether the change is obviously correct and trivially verifiable.
• I have read and followed the contribution guidelines.