feat(tests): Add tests for ecadd/ecmul/ecpairing constant gas repricing

[pdobacz]

🗒️ Description

The precompiles were repriced in Istanbul. There are legacy tests covering this but are hard to port, while (given static tests) we're only missing pre-istanbul price calculation coverage.

This test fills this gap but doesn't otherwise port the legacy test.

🔗 Related Issues or PRs

N/A.

✅ Checklist

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

  uvx tox -e static

• 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: Set appropriate labels for the changes (only maintainers can apply labels).

[codecov-commenter]

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.07%. Comparing base (9563a51) to head (6bbf8d4).
⚠️ Report is 2 commits behind head on forks/osaka.
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Additional details and impacted files

@@             Coverage Diff              @@
##           forks/osaka    #1738   +/-   ##
============================================
  Coverage        86.07%   86.07%           
============================================
  Files              743      743           
  Lines            44078    44078           
  Branches          3894     3894           
============================================
  Hits             37938    37938           
  Misses            5659     5659           
  Partials           481      481           

Flag	Coverage Δ
unittests	86.07% <ø> (ø)

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