Inelegant decoders

[gabedonnan]

In the current iteration of Pythereum, dataclasses are managed using dataclass_json with decoder functions for each custom data type. While this solution works, the more different data types that are introduced, the more decoder functions need to be produced and tested. The functions are fairly inelegant and could be made more generic or an entirely different object construction route could be taken. Any suggestions on this would be welcome.