Add Tonga holidays

[PPsyrius]

Proposed change

Add Tonga holidays (en_US, to localization).

Closes #1288.

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/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 added references to all holidays information sources used in this PR
• The code style looks good: make pre-commit command generates no changes
• All tests pass locally: make test, make tox (we strongly encourage adding tests to your code)

[PPsyrius]

This PR is marked as a draft should self._add_anzac_day(name) be added via #1531 - any help simplifying the holiday triggers would be greatly appreciated here. 👀

[coveralls]

Pull Request Test Coverage Report for Build 6710875690

• 78 of 78 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 99.978%

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Totals
Change from base Build 6678081414:	0.0%
Covered Lines:	10143
Relevant Lines:	10143

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💛 - Coveralls

[KJhellico]

@PPsyrius , that's great! A new and exciting country! Please look at some refactoring suggestions.

[KJhellico]

I have some doubts about the exact meaning of Tonga observed holidays. Is it just an extra day off or is the actual celebration being moved (as in Latin America)? Especially in cases of moving to Monday from other working days. Maybe we should use _move_holiday()?

[PPsyrius]

I have some doubts about the exact meaning of Tonga observed holidays. Is it just an extra day off or is the actual celebration being moved (as in Latin America)? Especially in cases of moving to Monday from other working days. Maybe we should use _move_holiday()?

I'm rechecking this at the moment, considering the lack of information in general.

The gov website dictates that Nov 4, 2023 - the actual date itself, is also an holiday, at least for Tonga's Ministry of Communications for example, though other evidence i.e. Matangi Tonga Online does indeed points towards LatAm implementation for 2021-2022 for the general public.

@arkid15r @KJhellico Please let me know which way implementation better aligns with actual situation here 👀

[PPsyrius]

Update: I'm going with the move_holiday method for now, then adding them back if those three holidays fall on their actual date for GOVERNMENT category - seems like the best compromise for this one, which fits both public and gov calendar available online.

Edit: simply picking the non-observed option would've gotten the same effect as what we're looking for in the government calendar, thus not implemented.

[arkid15r]

LGTM in general, here are my readability/consistency improvement suggestions:

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
12 Code Smells

No Coverage information
No Duplication information

[arkid15r]

🇹🇴 LGTM