Add Bosnian Cyrillic (ijekavica) date translations

[branislavroljic]

This PR adds Bosnian Cyrillic ijekavian variants to bs-Cyrl via supplementary date translation data.

The existing ekavian forms are left unchanged; ijekavian forms are added as additional valid variants to improve coverage for Bosnian users.

Testing:

• Ran tox locally (pre-commit and docs pass; remaining failures are known Windows-specific issues)
• Manually verified parsing of new phrases using locales=["bs-Cyrl"]

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.56%. Comparing base (b7bb1a5) to head (afa6a33).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1293      +/-   ##
==========================================
- Coverage   96.60%   96.56%   -0.04%     
==========================================
  Files         235      235              
  Lines        2886     2886              
==========================================
- Hits         2788     2787       -1     
- Misses         98       99       +1     

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