fix: BuildCompilerFromPool function overloading type errors

[gianmarco27]

Here i am once again!
The function overload definition edit suggested in #156 brought additional type errors in fastify because of how ts handles signatures overload.

What i did:

1. Added more tests to reproduce the different usages.
2. Tested reverting to the old function declarations that were in place before fix: enrich type definition of buildCompilerFromPool method #156, which failed the new tests.
3. Tested various approaches with interface and types to try and preserve the function signature overloading logic.
4. Finally changed approach to manually define a single function signature, with the type union for the specific parameter, without actually using signature overload.

It works, but what did it cost?

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

[mcollina]

lgtm

[Eomm]

It makes sense - but it was making sense before too 😄