zkevm: reconsider the need of a fixture format for stateless validator

Creating this issue to track a potential discussion for the future after some things settle. Mainly, using a new fixture format for stateless runs which can allow a bit of bloating of the current `blockchain_tests` fixture format modifications.

We have intentionally avoiding this for now to avoid adding complexity to our current changes and requiring ELs to support a new format. But at some point after we finish doing most of the work on the spec/testing side and see all the cards in the table, we can reconsider this decision and potentially create a new format that can leave things cleaner on the `blockchain_test` format if we think make sense.

Please see the PR description of https://github.com/ethereum/execution-specs/pull/2872#issue-4470158484 for some extra context.