build(test): add pytest-xdist for parallel test execution

[tiran]

Pull Request Description

What

Add pytest-xdist to test dependencies and configure 3 parallel workers via addopts. Testing showed that 4 or more workers does not provide measurable benefits.

See https://pytest-xdist.readthedocs.io/en/stable/

Why

Speed up local testing. On my machine, unit tests now takes less than 4 seconds instead of 12 seconds.

• PR follows CONTRIBUTING.md guidelines

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📥 Commits

Reviewing files that changed from the base of the PR and between 694f04f and 3c92bb0.

📒 Files selected for processing (1)

• pyproject.toml

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📝 Walkthrough

Walkthrough

pyproject.toml now includes pytest-xdist in the test extra. Pytest is configured with addopts = "-n 3", which sets the default xdist worker count to three.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~2 minutes

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly states the main change: adding pytest-xdist for parallel test execution.
Description check	✅ Passed	The description matches the change by explaining the new dependency, 3-worker configuration, and the performance goal.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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[rd4398]

Looks good to me! For some reason CI is failing :(

[mergify]

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[tiran]

Yes, there is an issue with coverage and xdist. I have a local fix, but I haven't pushed it yet.

I'm creating a new PR.