feat: automate changelog updates in pypi-publish workflow

[ghinks]

This PR automates the process of updating the CHANGELOG.md file whenever a new version is published to PyPI.

Changes:

• CHANGELOG.md: Initialized a new changelog file with a standard template.
• .github/workflows/pypi_publish.yml:
  • Added a new Update Changelog step that:
    • Identifies the previous version tag.
    • Extracts commit messages between the previous tag and HEAD.
    • Formats and prepends these changes to CHANGELOG.md under a new version heading.
  • Updated the Commit Patch Bump step to include the updated CHANGELOG.md in the automatic version bump commit.

This ensures that the project history is consistently maintained without manual intervention during the release process.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Use tag before HEAD when deriving changelog range

When this workflow runs on the release trigger, checkout is at the release tag commit, so git describe --tags --abbrev=0 resolves to that same tag. The subsequent range ${PREVIOUS_TAG}..HEAD is therefore empty, which produces changelog entries without the commits for the released changes. This makes release notes inaccurate specifically for tag-triggered publishes.

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