fix(types): make definitions `nodenext` compatible

[SuperchupuDev]

Fixes #223

Checklist

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

[Uzlopak]

Do we have a typing test for this?

[Uzlopak]

CI is failing.

[SuperchupuDev]

I tried fixing the tests but the error messages are really complex for a person that doesn't know much about fastify's internals. Adding Partial<> to some types in the failing tests worked but I don't think that's an actual fix. Would anyone be willing to fix the tests, or at least point to the correct direction?

[Uzlopak]

@SuperchupuDev @climba03003

I fixed the typings.