fix: exclude current year-end weekly period [DHIS2-21585]

[eirikhaugstulen]

Summary

Fixes DHIS2-21585 by preventing getAdjacentFixedPeriods from returning the current weekly period when stepping backwards from the final week of a year.

Root Cause

The weekly backward traversal searched for the first period with a start date after the current period. When the current period was the last generated week in the year, no later start date existed, so the slice boundary fell at the end of the year and included the current period again.

Changes

• Treat the first current-or-following weekly period as the exclusive end boundary when collecting previous periods.
• Normalize the following-period boundary when no later period exists in the current generated year.
• Add a Gregorian regression test for stepping back from 2023W52 to 2023W51.

Validation

• yarn test get-adjacent-fixed-periods.gregorian.spec.ts --watchAll=false --runInBand --watchman=false
• yarn test get-adjacent-fixed-periods --watchAll=false --runInBand --watchman=false
• yarn test --watchAll=false --runInBand --watchman=false
• yarn build:types
• yarn d2-style check changed files

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
2.1% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.89%. Comparing base (d202f08) to head (3099975).

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #95      +/-   ##
==========================================
+ Coverage   90.87%   90.89%   +0.02%     
==========================================
  Files          57       57              
  Lines        1249     1252       +3     
  Branches      352      353       +1     
==========================================
+ Hits         1135     1138       +3     
  Misses        112      112              
  Partials        2        2              

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