Add official NeMo RL container support and validation for GB300

## Summary

Add official NeMo RL container support for NVIDIA GB300 hardware.

## Requested scope

- Validate the official NeMo RL container on GB300.
- Provide and document recommended GB300 configuration.
- Add appropriate GB300 test coverage where infrastructure permits.
- Publish representative GB300 baseline performance results in the performance documentation.

## Acceptance criteria

- An official NeMo RL container is validated on GB300.
- Recommended configuration and any known limitations are documented.
- GB300 validation or regression coverage is in place.
- GB300 baseline performance results are included in the performance summary.