chore(main): release 6.0.0-rc.2 (#664)

## Summary
- Trigger release-please to create the 6.0.0-rc.2 release
- Includes SageMaker transport extraction to separate
`deepgram-sagemaker` package
- Includes unused import cleanup in socket clients

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Author: lukeocodes