Optimization: Recursive Protobuf Serialization/Deserialization

[farbodahm]

In the PR #35, I introduced a recursive way for serializing/deserializing Records to Protobuf messages (while adding ArrayTypes).

It's also possible to rewrite that functionality without recursion (while assuming ArrayType only contains one type).
For the sake of simplicity, For now I keep that functionality. But we need to benchmark, verify and make sure that it's not creating a performance overhead for our engine.