Add pre-commit hooks for ruff and lint code

[slackline]

The recently added switch to pyproject.toml (see #7 ) included configuration options for the ruff.

The easiest way to add this to the development workflow is via pre-commit and pre-commit.ci which runs the checks as part of the Continuous Integration.

Tasks to complete...

• Tidy up the dev section of project.optional-dependencies in pyproject.toml. Currently there is not test-suite and there are some extraneous packages in there, at a bare minimum dev should retain ruff and
• Add .pre-commit-config.yaml with appropriate configuration options for ruff
• Apply linting to the code base and resolve all issues. #11
• Ensure there is the appropriate configuration section for pre-commit.ci in the .pre-commit-config.yaml
• Allow permission for pre-commit.ci to run on this repository.

Might also be worth linting the code with pylint as ruff doesn't always pick up all the "code smells"

• Add pylint to dev section of project.optional-dependencies.
• Add a .pylintrc to configure how pylint runs on the repository.
• Add a local hook to .pre-commit-config.yaml and ensure this is excluded from pre-commit.ci (typically required because the environment that runs on pre-commit.ci won't have all of the required dependencies to run the linting).