Fix remaining Python 3.9 incompatible type annotations in backend packages
that were causing test failures. The union operator (|) syntax for type hints
was introduced in Python 3.10 and causes "TypeError: unsupported operand
type(s) for |" errors in Python 3.9.
Changes in leann-backend-diskann:
- Convert zmq_port: int | None to Optional[int] in diskann_backend.py
- Convert passages_file: str | None to Optional[str] in diskann_embedding_server.py
- Add Optional imports to both files
Changes in leann-backend-hnsw:
- Convert zmq_port: int | None to Optional[int] in hnsw_backend.py
- Add Optional import
This resolves the final test failures related to type annotation syntax and
ensures full Python 3.9 compatibility across all packages.
🤖 Generated with [Claude Code](https://claude.ai/code)
Co-Authored-By: Claude <noreply@anthropic.com>
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