Support tests in `ethereum-spec-new-fork`

Post #1372 the new fork tool no longer supports tests. After welding this repository with the EEST repository, we should bring back support for automatically duplicating the tests.

<a href="https://discord.com/channels/1359927674746835211/1408155653096210534"><img width="1000" height="1460" alt="Image" src="https://github.com/user-attachments/assets/53f5c444-fabe-4c06-91f8-f310c6a694f4" /></a>