fix: Improve pyproject.toml output and keep workflow more consistent

[xmnlab]

Pull Request description

• organize build-system files into folders, one folder for each build-system
• add test to check if the package is importable and if it shows the correct version using __version__ (not working yet for mesonpy and maturin)
• standardize cpp file names
• fix the structure in the final version of pyproject.toml
• fix some issues with some build system configurations
• fix the end of file in the post generation hook

How to test these changes

• ...

Pull Request checklists

This PR is a:

• bug-fix
• new feature
• maintenance

About this PR:

• it includes tests.
• the tests are executed on CI.
• the tests generate log file(s) (path).
• pre-commit hooks were executed locally.
• this PR requires a project documentation update.

Author's checklist:

• I have reviewed the changes and it contains no misspelling.
• The code is well commented, especially in the parts that contain more
  complexity.
• New and old tests passed locally.

Additional information

Reviewer's checklist

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## Reviewer's Checklist

- [ ] I managed to reproduce the problem locally from the `main` branch
- [ ] I managed to test the new changes locally
- [ ] I confirm that the issues mentioned were fixed/resolved

[github-actions]

🎉 This PR is included in version 0.8.2 🎉

The release is available on:

• 0.8.2
• GitHub release

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