docs: update README.md for v1.8.0 with breaking changes

- Add comprehensive v1.8.0 changelog with breaking changes section
- Document async consumer commit requirement with before/after examples
- Update basic consumer example to show new async commit syntax
- Highlight major improvements: manual commit testing, error messages, dependencies
- Add clear migration guidance for users upgrading to v1.8.0

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Co-Authored-By: Claude <noreply@anthropic.com>