feat(CI): add upgrade test

[kamuikatsurgi]

Description

Adds a workflow that tests rolling upgrades of bor on a PoS devnet. Deploys a devnet with :latest images, builds bor:local from the PR code, runs the upgrade script to roll all nodes from :latest to bor:local, then runs a post-upgrade health check (block production, node sync, milestones, checkpoints, L1→L2 bridge state syncs).

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 49.62%. Comparing base (6b0405c) to head (697afb1).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2070      +/-   ##
==========================================
- Coverage   49.65%   49.62%   -0.03%     
==========================================
  Files         873      873              
  Lines      150641   150641              
==========================================
- Hits        74803    74761      -42     
- Misses      70782    70822      +40     
- Partials     5056     5058       +2     

see 13 files with indirect coverage changes
see 13 files with indirect coverage changes

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud