Replace pylint with ruff for linting and formatting

[janhoy]

Summary

The project currently uses pylint (.pylintrc) for linting. Replace it with
ruff, a significantly faster tool that covers linting
and formatting (replacing black/isort) in a single dependency.

Motivation

• Apache Airflow adopted ruff as its primary Python quality tool ([tool.ruff] in
  pyproject.toml)
• Ruff is 10–100× faster than pylint, enabling faster CI and pre-commit hooks
• Covers the same (and broader) rule set as pylint + isort + black in one config block
• Configuration lives in pyproject.toml alongside other tool config

Proposed changes

1. Add pyproject.toml with [tool.ruff] linting and [tool.ruff.format] sections
2. Remove .pylintrc
3. Update Makefile lint target to invoke ruff check . and ruff format --check .
4. Update tox.ini / CI to use ruff
5. Fix any new lint findings surfaced by ruff

References

• https://docs.astral.sh/ruff/
• Apache Airflow pyproject.toml as a reference configuration