Update China holidays add non-statutory holidays support, l10n, optional half-day holidays

[PPsyrius]

Proposed change

Add non-statutory (but part of official public holiday allotment) observed holidays, as well as HALF-DAY category and general l10n support (en_US, th, zh_CN, zh_TW).

The following implementation is cross-checked with official sources from 2001-2023, with earlier date implementation based on the relevant section of the 1949 and 1999 revisions of the Chinese Holiday Act.

Happy Mid-Autumn Festival! 🌔 🥮

Closes #1475 .

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
• This PR is filed against beta branch of the repository
• This PR doesn't contain any merge conflicts and has clean commit history
• 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)
• The related documentation has been added/updated (check off the box for free if no updates is required)

[coveralls]

Pull Request Test Coverage Report for Build 6427501304

• 134 of 134 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.02%) to 99.977%

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Totals
Change from base Build 6413773841:	-0.02%
Covered Lines:	9651
Relevant Lines:	9651

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💛 - Coveralls

[PPsyrius]

Coverall appears to have some issue with this particular line for some reason and I'm at my wit's end here

[arkid15r]

It's a great PR -- a lot of work towards CN holidays improvement! It feels like a whole new country support has been added 👍

Here are some suggestions on how we could make the code better:

[arkid15r]

Let's deal with this first and take care of the coverage after that.

[arkid15r]

LGTM