PULL_REQUEST_TEMPLATE.md

What & why

Checklist

• make ci passes locally (lint → collection → tests → coverage ≥ 92%)
• New/changed public API has docstrings and is exported in the subpackage __init__.py
• Tests added or updated
• CHANGELOG.md updated under [Unreleased]
• Added yourself to CONTRIBUTORS.md (skip if you would rather not be listed)