Add GitHub action to publish to PyPI

[Adam-D-Lewis]

This commit adds automated PyPI publishing capabilities following the same approach used by the Nebari project:

• Configure hatch-vcs for automatic version generation from git tags
• Add GitHub Actions workflow for publishing to PyPI on release
• Workflow tests on TestPyPI before publishing to production
• Uses OIDC-based trusted publishing for secure package deployment
• Update version management to use _version.py instead of about.py
• Add _version.py to .gitignore as it's auto-generated

🤖 Generated with Claude Code

Reference Issues or PRs

What does this implement/fix?

Put a x in the boxes that apply

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds a feature)
• Breaking change (fix or feature that would cause existing features not to work as expected)
• Documentation Update
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no API changes)
• Build related changes
• Other (please describe):

Testing

• Did you test the pull request locally?
• Did you add new tests?

Documentation

Access-centered content checklist

Text styling

• The content is written with plain language (where relevant).
• If there are headers, they use the proper header tags (with only one level-one header: H1 or # in markdown).
• All links describe where they link to (for example, check the Nebari website).
• This content adheres to the Nebari style guides.

Non-text content

• All content is represented as text (for example, images need alt text, and videos need captions or descriptive transcripts).
• If there are emojis, there are not more than three in a row.
• Don't use flashing GIFs or videos.
• If the content were to be read as plain text, it still makes sense, and no information is missing.

Any other comments?