chore(tests): fix modexp conftest for tx gas limit cap

[spencer-tb]

🗒️ Description

Fixes the tx gas limit cap (from EIP-7825) for ModExp (EIP-7883) tests.

🔗 Related Issues or PRs

#2108

✅ Checklist

• All: Ran fast tox checks to avoid unnecessary CI fails, see also Code Standards and Enabling Pre-commit Checks:

  uvx --with=tox-uv tox -e lint,typecheck,spellcheck,markdownlint

• All: PR title adheres to the repo standard - it will be used as the squash commit message and should start type(scope):.
• All: Considered adding an entry to CHANGELOG.md.
• All: Considered updating the online docs in the ./docs/ directory.
• All: Set appropriate labels for the changes (only maintainers can apply labels).

[marioevz]

I added a raise Exception to make the test fail if the gas limit went above the cap, but none of the tests failed, even with #2108 applied on top of these changes, so I might be missing something.
What's the steps to reproduce the issues for which this fix is needed?

[spencer-tb]

I added a raise Exception to make the test fail if the gas limit went above the cap, but none of the tests failed, even with #2108 applied on top of these changes, so I might be missing something. What's the steps to reproduce the issues for which this fix is needed?

Sorry yeah. We need to add this case manually:
("00" * 32, "00" * 1024, "01" * 1024, "00" * 1023 + "01", "Z16"),

I thought it was in the PR. Will push it just now.

[LouisTsai-Csie]

Nice! I will try the remaining refactoring in my PR, thanks for this

[marioevz]

See my comment, I think current solution could be improved because future changes might break tests if we are not careful.

[marioevz]

LGTM, thanks!