Improved UTF encoding processing

[fktn-k]

This PR has improved the UTF encoding processing, including the following changes:

• rename utf8_encoding.hpp as utf_encodings.hpp for future modifications
• use uint8_t as UTF-8 byte values instead of char to avoid potential issues from signed/unsigned conversions
• run byte swaps in one call related to the little/big endianness.

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Pull Request Checklist

Read the CONTRIBUTING.md file for detailed information.

• [x] Changes are described in the pull request or in a referenced issue.
• [x] The test suite compiles and runs without any error.
• [x] The code coverage on your branch is 100%.
• [x] The documentation is updated if you added/changed a feature.

Please don't

• The C++11 support varies between different compilers and versions. Please note the list of supported compilers. Some compilers like GCC 4.7 (and earlier), Clang 3.3 (and earlier), or Microsoft Visual Studio 13.0 and earlier are known not to work due to missing or incomplete C++11 support. Please refrain from proposing changes that work around these compiler's limitations with #ifdefs or other means.
• Please refrain from proposing changes that would break YAML specifications. If you propose a conformant extension of YAML to be supported by the library, please motivate this extension.
• Please do not open pull requests that address multiple issues.

[github-actions[bot]]

:octocat: Upload Coverage Event Notification

Coverage data has been uploaded for the commit 29794f6ec21c2e841adb534ebeb8aad6bdb19832. You can download the artifact which contains the same file uploaded to the Coveralls and its HTML version.

Name	fkYAML_coverage.pr318.zip
ID	1433278777
URL	https://github.com/fktn-k/fkYAML/actions/runs/8773164060/artifacts/1433278777

[coveralls]

Pull Request Test Coverage Report for Build 8773164060

Details

• 215 of 215 (100.0%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

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Totals
Change from base Build 8770978537:	0.0%
Covered Lines:	3526
Relevant Lines:	3526

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💛 - Coveralls