Switch project to use pyproject.toml

[hagenw]

This modernizes the Python infrastructure of the project:

• Replace setup.py and setup.cfg by pyproject.toml
• Replace PEP8 checking in pre-commit with flake8 by ruff
• Add checking for common spelling errors with codespell in pre-commit

As part of the corrections of the ruff detected errors, audb.Dependencies.__len__() was added to the documentation:

[codecov]

Codecov Report

Merging #316 (304321a) into main (e2a3231) will not change coverage.
The diff coverage is 100.0%.

Impacted Files	Coverage Δ
audb/core/conftest.py	100.0% <ø> (ø)
audb/core/flavor.py	100.0% <ø> (ø)
audb/core/publish.py	100.0% <ø> (ø)
audb/__init__.py	100.0% <100.0%> (ø)
audb/core/api.py	100.0% <100.0%> (ø)
audb/core/config.py	100.0% <100.0%> (ø)
audb/core/dependencies.py	100.0% <100.0%> (ø)
audb/core/info.py	100.0% <100.0%> (ø)
audb/core/load.py	100.0% <100.0%> (ø)
audb/core/load_to.py	100.0% <100.0%> (ø)
... and 1 more