chore: add jsdoc tags

[Fdawgs]

Without the tags, VS Code's IntelliSense could not provide autocomplete, parameter hints, or type checking when working in the codebase, which made contributing harder than it needed to be.

This probably also helps other IDEs.

Checklist

• run npm run test && npm run benchmark --if-present
• documentation is changed or added
• commit message and code follows the Developer's Certification of Origin
  and the Code of conduct

[Copilot]

Pull request overview

This PR adds JSDoc/type annotations across the Fastify bearer-auth plugin code to improve editor IntelliSense (autocomplete, parameter hints, and type checking) when working in the JS codebase.

Changes:

• Added JSDoc blocks and import('../types/index')-based type annotations for the main plugin and auth factory functions.
• Documented helper/auth functions (compare, authenticate, handleUnauthorized) with JSDoc params/returns.
• Refactored lib/compare.js to import timingSafeEqual via destructuring.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
lib/verify-bearer-auth-factory.js	Adds JSDoc/type annotations for the factory and internal helper(s).
lib/compare.js	Adds JSDoc for constant-time comparison and refactors crypto import.
lib/authenticate.js	Adds JSDoc for key authentication helper.
index.js	Adds a top-level JSDoc/type annotation for the exported plugin function.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

You can also share your feedback on Copilot code review. Take the survey.