fix: preserve annotations across table groups

[masonkatz]

Summary

• retain annotations at struct-type boundaries
• emit all annotations sharing a row position in insertion order
• add regression coverage for both cases

Fixes #2

Validation

• make test
• make lint (currently reports five pre-existing goconst findings on origin/main)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.28%. Comparing base (8a905d7) to head (2a8e909).

Additional details and impacted files

@@            Coverage Diff             @@
##             main       #6      +/-   ##
==========================================
+ Coverage   78.06%   80.28%   +2.21%     
==========================================
  Files           8        8              
  Lines         269      284      +15     
==========================================
+ Hits          210      228      +18     
+ Misses         55       52       -3     
  Partials        4        4              

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