pytest-xdist is not declared in the test extra, the lockfile or any workflow #1265

Where: pyproject.toml (test extra), requirements-lock.txt, .github/workflows/audits.yml.

Current gap: make setup now installs pytest-xdist for the parallel make test-fast, but the test extra, the lockfile and the CI test jobs do not mention it, so a contributor who installs the extra gets the serial run and CI never benefits.

Suggested approach: Add pytest-xdist to the test extra and the lockfile (keeping test_declared_dependencies and test_dependency_versions green) and use -n auto in the CI test step if it measurably helps.

Done when: pip install -e '.[test]' makes make test-fast parallel and CI's test time is compared before and after.