feat(data_plane): add Mooncake GDR support

[zyzhou5]

What does this PR do?

Adds the minimal NeMo-RL configuration plumbing needed to enable TransferQueue v0.1.9's Mooncake GPUDirect RDMA (GDR) path. TransferQueue v0.1.9 is already pinned on current main by #3423.

• adds optional data_plane.use_gdr; omitting it defaults to false, so existing recipes are unchanged;
• passes protocol: rdma and use_gdr: true to Mooncake when GDR is enabled;
• leaves RDMA device selection local to each Mooncake client unless explicitly configured;
• requires CUDA to be initialized before a GPU worker attaches its GDR-enabled TQ client, avoiding TQ's CPU fallback;
• retains NeMo-RL's existing transfer/decode paths and TQ's default staging-buffer size; and
• documents how users select TCP, CPU RDMA, or GPU RDMA.

Persistent queued Mooncake objects remain in CPU RAM. GDR changes the CUDA client's transfer path by using a registered GPU staging buffer; it does not turn the persistent queue into GPU storage.

User configuration

data_plane:
  enabled: true
  impl: transfer_queue
  backend: mooncake_cpu
  use_gdr: true

Relationship to #2935

This PR does not stack on or require #2935. The TQ dependency update is already on main via #3423. The runtime-environment cleanup proposed by #2935 is separate and is not included here.

Relationship to #3837

To use GDR on the put side instead of falling back to CPU RDMA, we need #3837 to get merged since TQ must be initialized inside the generation worker after CUDA is initialized so it selects GDR for PUTs.

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[zyzhou5]

/ok to test d2edefb

[zyzhou5]

/ok to test 31f9117

[zyzhou5]

/ok to test 5bdc8e7