chore: use files allow list for the published package

[slagiewka]

Eliminates .github, benchmarks, test, types test and config files from the root.
I know that some maintainers want to ship test with the package, I can re-add the directory if needed.

Before

npm pack --dry-run
npm warn gitignore-fallback No .npmignore file found, using .gitignore for file exclusion. Consider creating a .npmignore file to explicitly control published files.
npm notice
npm notice 📦  @fastify/error@4.2.0
npm notice Tarball Contents
npm notice 80B .gitattributes
npm notice 1.4kB .github/dependabot.yml
npm notice 651B .github/workflows/ci.yml
npm notice 293B .github/workflows/lock-threads.yml
npm notice 1.1kB LICENSE
npm notice 5.5kB README.md
npm notice 319B benchmarks/create.js
npm notice 1.1kB benchmarks/instantiate.js
npm notice 547B benchmarks/no-stack.js
npm notice 373B benchmarks/toString.js
npm notice 135B eslint.config.js
npm notice 2.7kB index.js
npm notice 1.7kB package.json
npm notice 6.8kB test/index.test.js
npm notice 10.0kB test/instanceof.test.js
npm notice 1.4kB types/index.d.ts
npm notice 5.3kB types/index.tst.ts
npm notice Tarball Details
npm notice name: @fastify/error
npm notice version: 4.2.0
npm notice filename: fastify-error-4.2.0.tgz
npm notice package size: 8.5 kB
npm notice unpacked size: 39.4 kB
npm notice shasum: aec6d155bf1cfe07917e8dcb28e9c7fff6689d79
npm notice integrity: sha512-LZoHiXtXvoyU3[...]LuGCXBD3XGUXg==
npm notice total files: 17
npm notice
fastify-error-4.2.0.tgz

After

npm pack --dry-run
npm notice
npm notice 📦  @fastify/error@4.2.0
npm notice Tarball Contents
npm notice 1.1kB LICENSE
npm notice 5.5kB README.md
npm notice 2.7kB index.js
npm notice 1.7kB package.json
npm notice 1.4kB types/index.d.ts
npm notice Tarball Details
npm notice name: @fastify/error
npm notice version: 4.2.0
npm notice filename: fastify-error-4.2.0.tgz
npm notice package size: 3.9 kB
npm notice unpacked size: 12.5 kB
npm notice shasum: 999df936f7db3ece53af515b6a0c2d81df72c63b
npm notice integrity: sha512-0Ns6kvtvAwwL2[...]zyzDoptZWQJwA==
npm notice total files: 5
npm notice
fastify-error-4.2.0.tgz

Checklist

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