Feat: optimizations with smallvec

[mrLSD]

Description

Added optimizations with smallvec crate. The intention is to reduce memory allocation when it possible.

One of the most significant problems for memory allocation and re-allocation is unknown size of data. To mitigate it, we can allocate on the stack for arrays, when size is known. And reallocate memory on the heap for program and algorithm needs. smallvec solves it good enough.

Simulation results

It was tested through aurora-engine tests. It shows insignificant NEAR gas consumption improvement.

⚠️ Notes

As NEAR gas consumption improved insignificantly, I don't mind if there are some arguments against this solution.

[birchmd]

Thanks for looking into this potential optimization. I think it is fine to merge it even if the impact is low.

I also think it makes sense that this optimization does not save much gas because it always saves exactly one memory allocation per call to Aurora Engine (the first one where the call stack is initialized). SmallVec allows us to skip the first allocation but if the call stack gets deeper than DEFAULT_CALL_STACK_CAPACITY then a new allocation is required (both in the old code and with this optimization). I think SmallVec usually is more important when there is a lot of churn on the data being allocated (e.g. a small Vec was being allocated in a function that is called many times or as part of a loop).