Update Cambodia holidays: add Peace Day in Cambodia

[PPsyrius]

Proposed change

• Add "Peace Day in Cambodia" (ទិវា​សន្តិភាព​នៅ​កម្ពុជា​) for Cambodia from 2024 onwards, English translation is based from the unofficial translation in the link above and https://www.acledabank.com.kh/kh/eng/md_publicholiday . (Simply referring to "Peace Day" alone could be confusing as Cambodia already has another ex-holiday called "Paris Peace Agreement's Day")
• More test case refractors as previously recommended in Update Thailand holidays in 2025 #2081 .

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 holidays functionality in general)

Checklist

• I've followed the contributing guidelines
• I've successfully run make check, all checks and tests are green

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (60966ea) to head (a44af0b).
Report is 5 commits behind head on dev.

Additional details and impacted files

@@            Coverage Diff            @@
##               dev     #2108   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          192       192           
  Lines        11577     11579    +2     
  Branches      1741      1742    +1     
=========================================
+ Hits         11577     11579    +2     

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[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

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

See analysis details on SonarCloud

[PPsyrius]

I'm thinking of adding some kind of hidden char remover to the pre-commit later to prevent that from being included in the first place again. 👀

[KJhellico]

LGTM.

[arkid15r]

Thanks for the cleanup 👍