Implement single-rollout asynchronous optimization

### Method description

https://arxiv.org/abs/2607.07508

### Open source status

- [ ] The method implementation is available
- [ ] The model weights are available
- [ ] The training datasets are available

### Provide useful links for the implementation

https://arxiv.org/abs/2607.07508

@think2try is a paper author

Start by reading the linked paper to understand the single-rollout asynchronous optimization method, then inspect TRL's existing training entry points for the appropriate integration point. Done means the method implementation is available in the repository; the issue also records whether model weights and training datasets are available.

Written by the indexing model from the issue text.