Handle `from ...module` imports

[tcompa]

We can e.g. decide that

from ..module import thing

is acceptable up to two dots, and add a precommit rule for three dots or more.

[tcompa]

Rather than setting up a flake8 plugin, we can perhaps move directly to https://docs.astral.sh/ruff/settings/#lint_flake8-tidy-imports_ban-relative-imports (with the "parents" option).
TBD