Refactor CloudOoo tests.

- Each class now correspond to an instance with different configuration,
and possibly several test methods.
- Upgraded to more recent pypdf version.
- The code has been reviewed to reduce complexity and repetition.
- Adds documentation to all public functions, in Google style.
- Some other cosmetic changes have been made for
consistency (consistent parentheses indentation, consistent string
literal quotes), courtesy of ruff.

See merge request nexedi/slapos!1628