Apply node properties for the root node

[fktn-k]

fkYAML currently ignores node properties for the root node unintentionally, like parsing the following valid YAML snippet:

--- !!map
foo: bar

They are obviously allowed in the spec.
So this PR has fixed the serializer/deserializer to properly handle them and added some test cases to validate the changes.

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Pull Request Checklist

Read the CONTRIBUTING.md file for detailed information.

• Changes are described in the pull request or in a referenced issue.
• The test suite compiles and runs without any error.
• The code coverage on your branch is 100%.
• 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]

Upload Coverage Event Notification

Coverage data has been uploaded for the commit e934d700df7a612226900ce63b874fb02b2dc887.
You can download the artifact which contains the same file uploaded to the Coveralls and its HTML version.

Name	fkYAML_coverage.pr370.zip
ID	1823046897
URL	https://github.com/fktn-k/fkYAML/actions/runs/10432953001/artifacts/1823046897

[coveralls]

Pull Request Test Coverage Report for Build 10432953001

Details

• 19 of 19 (100.0%) changed or added relevant lines in 2 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 10429308281:	0.0%
Covered Lines:	3971
Relevant Lines:	3971

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💛 - Coveralls