Add regression tests for doc comment attribute formatting

[cknitt]

Adds the four examples from #6302 as formatter regression tests, verifying that single-line and multiline doc comments preserve the same attribute layout as normal comments. The underlying behavior was fixed in #7529.

Validation: make test-syntax, make test-syntax-roundtrip, and narrow-width formatting stability checks passed.

Closes #6302.

[chatgpt-codex-connector]

Codex Review Summary

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-04T10:00:48.853062Z	0b88b64	PR opened

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.32%. Comparing base (5c24235) to head (0b88b64).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8613      +/-   ##
==========================================
- Coverage   77.32%   77.32%   -0.01%     
==========================================
  Files         467      467              
  Lines       63342    63313      -29     
==========================================
- Hits        48982    48957      -25     
+ Misses      14360    14356       -4     

see 1 file with indirect coverage changes

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commit: 0b88b64

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