v0.2.0: Revamp data types

[jangko]

• Clear distinction between engine_api_types and eth_api_types
• Add convenience functions to handle V1, V2, and V3 of engine_api_types
• Add more tests

This PR is the first step toward using nim-json-serialization in nim-json-rpc.
More PR will come.

[arnetheduck]

Similar to how we have ssz tests, it would be good to have test cases with json examples of the objects that the serializer verifies can be read / written - we've had multiple cases of where the encoding inadvertedly was broken because of small changes to the codebase.

Ideally, @zah would also add support for strict mode for json-ser so that random serializers don't get included in the overload set for the ones that the standard encodings, as we've also had multiple cases of when nim-json-serialization uses the wrong encoding depending on what's imported or in which order.

[jangko]

I will add test from https://github.com/ethereum/execution-apis/tree/main/tests for eth_api, and also test cases for engine_api when we migrate to json-serialization.

[kdeme]

👍 👍 on the naming on eth_api_types.nim and engine_api_types.nim