Fix some miscellaneous issues breaking expectations/tests

[oerc0122]

• Accidentally labelled parse_args empty example as doctest causing failure with pytest --doctest-modules
• Force output to Path for required method in parse_single
• Make Block.get_lines add lines as elements of tuple rather than as characters.
• Fix issue with latest ruff version.
• Pin ruff version to avoid this problem in future

[ajjackson]

These seem fine and I don't mind them being batched as they are small and non-interactive.

Pinning an exact ruff version seems a bit aggressive, but I suppose as developers are not obliged to use the [lint] extra locally it's not the end of the world.