chore(go): update supported Go versions to 1.25.9 and 1.26.2

[ccojocar]

Summary

• Bump Go 1.26.1 → 1.26.2 in CI and release workflows
• Go 1.25.9 was already current — no change needed
• Source: https://go.dev/doc/devel/release

Files changed:

• .github/workflows/ci.yml (matrix + single-version steps)
• .github/workflows/release.yml (setup-go version)

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.15%. Comparing base (fa4824c) to head (bf3d691).
⚠️ Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1633      +/-   ##
==========================================
+ Coverage   81.07%   81.15%   +0.08%     
==========================================
  Files         108      108              
  Lines       10096    10110      +14     
==========================================
+ Hits         8185     8205      +20     
+ Misses       1426     1423       -3     
+ Partials      485      482       -3     

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