Consider extending test converage to execution-api tests

## Observation

The RPC layer is a part of the exposed API of the execution layer. Currently test vectors are being generated with geth and specified in execution-api.

## Suggestion

Still forming the idea, but it seems like this repo could generate those json outputs automatically for all of the blockchain tests already defined, increasing test coverage significantly.

Start by reading the existing execution-api test vectors and the blockchain tests whose outputs are generated with geth. Trace how the current JSON outputs and RPC-layer coverage are organized. Before implementation, define which existing blockchain tests should generate execution-api outputs automatically and how increased coverage will be measured.

Written by the indexing model from the issue text.