Prepare 4.2.1 release

[pfouque]

Description

Hotfix release

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update
• Other (no functional changes)

Checklist

• I have read the CONTRIBUTING.md guide
• Tests added/updated for the changes
• All tests pass locally (uv run pytest or pytest)
• Linting passes (uv run ruff check .)
• Documentation updated (if applicable)
• CHANGELOG.rst updated (for user-facing changes)

Testing

# Commands used to test
uv run pytest tests/test_xxx.py -v

Related Issues

[codecov]

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