declutter project configuration

[ArneBinder]

We should use pyproject.toml as much as possible. Also, there are some cases of duplicated and conflicting configuration.

Cases (files) to look into:

• .draglint - what is this about?
• .editorconfig - what is this about?
• .pre-commit-config.yaml - most of the packages are covered (regarding dependency versions) in pyproject.toml, but
  • what about prettier? And
  • what about all args?
• codecov.yml - but see existing codecov sections in pyproject.toml! what takes precedence and in which cases (local execution / CI)?