fix(types): option privacy in Nodenext | Node16

[Gehbt]

Relate commit #116

When use with typescript in compilerOptions: "module": "Node16" | "Nodenext", it will call the namespace fastifyCaching, that caused and should use

I don`t know why those tests-suits fail.

Checklist

• [ ] 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

Reproduction

• Stackblitz