feat(rollout): add VllmSamplerAdapter with Raiden weight sync support

[SurbhiJainUSC]

Summary

Adds VllmSamplerAdapter to integrate vLLM/TPU inference backends into Tunix distributed RL with native Raiden weight synchronization support.

Key Changes

1. VllmSamplerAdapter (vllm_sampler_adapter.py):
   • Implements the Sampler protocol and WeightSyncDestination interface for tpu-inference / RLVllmSampler.
   • Integrates the complete Raiden weight-sync lifecycle (bind_weight_sync, get_weight_sync_metadata, pre_weight_sync, weight_sync, post_weight_sync, abort_weight_sync, get_weight_sync_status).
2. RolloutManager (manager.py):
   • Instantiates VllmSamplerAdapter when sampler_type == "vllm".

DEPENDS ON #1990

Checklist

• I have added all the necessary unit tests for my change.
• I have verified that my change does not break existing code and all unit tests pass.
• I have added all appropriate doc-strings/documentation.
• My PR is based on the latest changes of the main branch (if unsure, rebase the code).
• I have signed the Contributor License Agreement.
• I have followed Contribution Guidelines.