Add 1991-2022 Russian substituted holidays

[PPsyrius]

Proposed change

Add 1991-2022 Russian substituted holidays, 1991-2025 Russian observed holidays.

Resolves #432 .

Type of change

• New country/market holidays support (thank you!)
• Supported country/market holidays update (calendar discrepancy fix, localization)
• Existing code/documentation/test/process quality improvement (best practice, cleanup, refactoring, optimization)
• Dependency update (version deprecation/pin/upgrade)
• Bugfix (non-breaking change which fixes an issue)
• Breaking change (a code change causing existing functionality to break)
• New feature (new python-holidays functionality in general)

Checklist

• I've followed the contributing guidelines
• I've run make pre-commit, it didn't generate any changes
• I've run make test, all tests passed locally

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (1a6a764) to head (8d4808e).
Report is 3 commits behind head on dev.

Additional details and impacted files

@@            Coverage Diff            @@
##               dev     #1957   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          188       188           
  Lines        11421     11422    +1     
  Branches      1794      1794           
=========================================
+ Hits         11421     11422    +1     

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[PPsyrius]

I don't think there's a way to reduce "new code duplication" for our test suite here without changing how def test_special_holidays(self) is coded, so ignore sonarcloud results for now.

[KJhellico]

@PPsyrius, thank you for this addition. Although I like researching substituted holidays in different countries, I prefer not to make changes to RU holidays myself for personal reasons.

If you are interested, you can look for more complete list here.

[PPsyrius]

@KJhellico Understandable, in any case I've expanded and updated Russian substituted holidays down to 1991, as well as adding in-lieu observance for 1991-2025 from the Wikipedia source you posted above. 🙏

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
1.6% Duplication on New Code

See analysis details on SonarCloud