pre-commit.ci has been disabled for a while.
This PR ensures that all the files has been validated/formatted by pre-commit, to avoid spurious diffs in subsequent PRs.
During the process, ruff broke the code because it removed an "unused" import which was actually used.
A linter which breaks my code is a linter which I cannot trust, so I just removed it. I re-enabled isort instead.
This re-enables CI tests on every PR 🎉.
This uses make test-integration, which runs tests sequentially.
In theory, we also have test-integration-parallel but it seems to be very flaky: many tests randomly timeout. I didn't spend too much time investigating this, it's probably worth its own investigation in a separate PR, but for now it's important to re-enable CI tests, even if they are a bit slower.
