Consider enabling INP ruff rules by default

[nathanjmcdougall]

Motivation
Missing __init__.py can cause problems for various tools, e.g. import-linter.
There's a question of whether this should be enabled by default or only when using import-linter. In any case, we should definitely try and re-add if it's been removed, when adding import-linter.
Disable it for the tests dir.

There's a repo which provides an autofix: https://github.com/lk16/detect-missing-init
But I'd be concerned about a different heuristic from ruff so I'm inclined to not use this. It's really an upstream ruff feature request.

Summary of desired enhancement
Enable the INP ruff rule as appropriate.