Fix #347: Rebuild pyproject.toml to adhere to PEP 621 & update poetry version

[sdruskat]

• Test that user agent name in utils is a combination of package name, version and homepage URL as per pyproject.toml
• Re-shuffle and rename sections
• Fix Update poetry to more recent version. #347: Update poetry build_backend to 2.3.1

Notes

• Test assumes that no other than the currently checked out version of hermes is installed in the workspace the tests are run from. This is because we're comparing distribution to declared metadata, and they may differ in real-life workspaces.
• pyproject.toml
  • Changed the license expression to include only software licenses for now.
  • Changed the homepage to hermes.software-metadata.pub (@zyzzyxdonta Does this break anything in terms of the user agent?)
  • Changed author order and edited the governance document to reflect order in CFF (currently the canonical source of authorship), as the ad-hoc change of the governance doc introduced incoherent metadata. (see Add authorship policy #408)
• Remove all poetry.tool-related tables from pyproject.toml, as these were superfluous:
  • The schema.json file doesn't even exist anymore
  • There's no need to explicitly declare the package. If we want to push to pypi-test, we can always adapt the manifest for this reason. I'd rather we reduce dependencies to the build_backend as much as possible.
  • ... apart from poetry's dependency group and optionality definitions 😠, becuase poetry still doesn't comply with PEP 735.
• Fixes the RTD build, which kept failing because it uses Python 3.10, no venv, and then expects toml to be present in the environment, which of course was only added to standard lib (tomllib) with 3.11.

[led02]

Some remarks made, looking good so far. Thanks for the great efford!

[led02]

⭐️⭐️⭐️⭐️⭐️
Great review experience, will review again!