v6.2.1

Key Highlights

• ONNX Runtime is now optional instead of required
• Explicit installation required for CPU: pip install onnxruntime
• Explicit installation required for GPU: pip install onnxruntime-gpu

Full Release Notes

- onnxruntime is now an optional dependency instead of required.

You now need to install ONNX Runtime explicitly:
`pip install onnxruntime`      # for CPU
`pip install onnxruntime-gpu`  # for GPU