Use Ruff linter and formatter

[ddundo]

Closes #54.

This PR introduces the Ruff linter and formatter to check for errors and stylistic issues, including the pre-commit hook. Relevant changes are done in pyproject.toml and .pre-commit-config.yaml. The rest of changes are due to applying the pre-commit.

A few things to note:

• I set the maximum line length to 79 as per PEP 8, but we can increase this if you prefer (personally I'm used to 88 and I find it to work well)
• At the moment I ignored quite a few errors that couldn't be fixed automatically (see the ignore list in pyproject.toml) - I'll open a separate issue to address these
• I added sample_data/ to .gitignore

I will change the target branch to develop if you create one (see #55).

[ddundo]

Copied this branch from my fork and opened a new PR #62.