use namespace runner instead of github runner on prs

[sobhe-Starkware]

Note

Low Risk
Low risk: changes only the GitHub Actions runner labels for existing formatting and test jobs, with no code or logic changes. Main risk is CI capacity/compatibility differences on the new Ubuntu 24.04 namespace runners.

Overview
Updates GitHub Actions workflows to run on namespace-provisioned Ubuntu 24.04 runners instead of ubuntu-latest.

check_formatting and verify_flows now use a small runner profile, while the main test job uses an xlarge runner profile to handle heavier workloads.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.80%. Comparing base (e29e2b7) to head (51b9297).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #103   +/-   ##
=======================================
  Coverage   95.80%   95.80%           
=======================================
  Files          43       43           
  Lines       10517    10517           
=======================================
  Hits        10076    10076           
  Misses        441      441           

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