Improvements to build and publish configuration

[ollipa]

I noticed that the project requires installing jinja2, pytest, setuptools, build, and wheel. jinja2, pytest, and setuptools were installed because they were defined as normal dependencies in pyproject.toml. The build workflow also called "poetry add" for build and wheel dependencies before creating the package, which made them end up in the requirements as well. This PR fixes those issues and also moves to a modern PEP 517 build process (using setup.py as a script is deprecated).

• Remove setup.py in favor of PEP 517 build via pyproject.toml
• Update GitHub Actions (checkout, setup-python) to v6
• Simplify release workflow to use 'poetry build'
• Move pytest and jinja2 to dev-dependencies
• Add dist/ to .gitignore

I tested the publishing workflow in my own fork against test-pypi (workflow run logs) and everything worked after changes.

[TKIPisalegacycipher]

Thank you for raising this, @ollipa. You are right, this was an area worth optimizing. We've resolved the issue with the following commits:

f87b44e
b8b7e66

Please let us know if you have any other suggestions and we'd be happy to review them! With this in mind, we will close this CR.