chore: upgrade to go1.26

[fredbi]

• remove build guards for go1.26
• regenerate code and docs to stop distinguishing go1.26 specifics
• lint: apply modernize

NOTE: go1.27 guards stay

Change type

Please select: 🆕 New feature or enhancement|🔧 Bug fix'|📃 Documentation update

Short description

Fixes

Full description

Checklist

• I have signed all my commits with my name and email (see DCO. This does not require a PGP-signed commit
• I have rebased and squashed my work, so only one commit remains
• I have added tests to cover my changes.
• I have properly enriched go doc comments in code.
• I have properly documented any breaking change.

[codecov]

Codecov Report

❌ Patch coverage is 97.61905% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 93.65%. Comparing base (2b009bf) to head (3ea5495).
⚠️ Report is 6 commits behind head on master.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
codegen/internal/generator/doc_generator.go	97.22%	1 Missing ⚠️
internal/assertions/compare.go	80.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #164      +/-   ##
==========================================
- Coverage   93.67%   93.65%   -0.03%     
==========================================
  Files         106      102       -4     
  Lines       13883    13884       +1     
==========================================
- Hits        13005    13003       -2     
- Misses        871      874       +3     
  Partials        7        7              

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