tests: add checks step-by-step for JSON NIVC

[Autoparallel]

Current tests we have test that the end output of the JSON parse/extract NIVC computation is correct. It is, however, possible that this chain could be correct while we regress on individual templates. So we should make sure that not even a single byte changes with those. I can foresee us having to change these templates to small issues we find (e.g., with slightly different JSON files that push this to its limit).