Chore: tests housekeeping

[shark0der]

Context

Several test setup improvements to keep things clean.

Changes proposed in this pull request

• Removes hardcoded berlin hardfork and fixes the tests that failed due to zero gas fee txes
• Simplifies accounts and signers generation and usage

Test plan

Only existing tests needed to pass.

Checklist

• Rebased the base branch
• Attached corresponding Github issue
• Prefixed the name with the type of change (i.e. feat, chore, test)
• Performed a self-review of my own code
• Followed the style guidelines of this project
• Made corresponding changes to the documentation
• Didn't generate new warnings
• Didn't generate failures on existing tests
• Added tests that prove my fix is effective or that my feature works

Review

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• 🍰 = Nice to have but not essential.
• 💡 = Suggestion or a comment based on personal opinion
• 🔨 = I believe this should be changed.
• 🤔 = I don’t understand something, do you mind giving me more context?
• 🚀 = Feedback