chore: upgrade to go 1.25.7

[skl]

Addressing CVE-2025-68121.

Documented how to upgrade the Go version in the new devdocs/go-version-upgrade.md.

[marctc]

thanks for the docs!

[skl]

#1316 will fix CI, I will publish a new obi-generator image directly from that branch.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 43.51%. Comparing base (ede9606) to head (4c8caca).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1315      +/-   ##
==========================================
- Coverage   43.52%   43.51%   -0.02%     
==========================================
  Files         305      305              
  Lines       32864    32864              
==========================================
- Hits        14305    14301       -4     
- Misses      17639    17643       +4     
  Partials      920      920              

Flag	Coverage Δ
integration-test	21.49% <ø> (-0.20%)	⬇️
integration-test-arm	0.00% <ø> (ø)
integration-test-vm-x86_64-5.15.152	0.00% <ø> (?)
integration-test-vm-x86_64-6.10.6	0.00% <ø> (?)
k8s-integration-test	2.36% <ø> (ø)
oats-test	0.00% <ø> (ø)
unittests	44.29% <ø> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.