Fix infinite recursion in abbrev_obj for circular references (#1)

* Fix infinite recursion in abbrev_obj for circular references

- Added visited parameter to _format_kvs to track visited objects
- Properly propagate visited set through all recursive calls
- Prevents infinite loops when objects contain circular references
- Added comprehensive test coverage for various circular reference scenarios

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

* Apply ruff formatting and fix pyright ignore placement

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Co-authored-by: Claude <noreply@anthropic.com>

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