Possible performance improvements

[MateuszKubuszok]

We are using Vector[Any] for building and storing the collection of overrides (both constant values and functions). Inside def addOverride we are using with +:.

• we might consider modifying the code to use :+ append instead instead - as it might be faster
• since TransformationContext does not depend on RuntimeDataStore we might also consider converting Vector to Array in some cases - inside the macro, once the Vector has all the values
• we might consider replacing Vector with some custom data structure that would be e.g. cheap to append, and on the first access computed internally an Array,
• any such change should still pass the tests and be verified with benchmarks - it might be possible that we would actually de-optimize the code or introduce a risky change without any benefits
  • if we consider compatibility issues - changing the +: to :+ happens inside the library code that could be evicted, but calling the apply(index) happens in the generated code that will stay the same, so it's a change that could be safely done only be recompiling the code, so it's a breaking change that could be introduced in future 2.0.0 release.