Define the project metadata in pyproject.toml instead of setup.cfg

[c-bata]

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Reference Issues/PRs

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What does this implement/fix? Explain your changes.

• Define the project metadata in pyproject.toml instead of setup.cfg.

[c-bata]

I tried to use setuptools_scm to simplify the release operation at 8c80c77.
However, as discussed in pypa/setuptools_scm#190, setuptools_scm's file_finders implicitly bundles SCM files with the source package. That is, .github, python_tests, tools, etc. are bundled with sdist. To exclude these files, I need to list the files to be excluded in MANIFEST.in or implement a fragile monkey patch in setup.py.

Therefore, I decided to avoid using setuptools_scm in this project.