[Mooncake] Defer PP hybrid KV group validation

[jianzs]

This PR adds a small follow-up fix on top of the source branch for vllm-project#46004.

Root cause: Mooncake validates per-KV-cache-group block counts before aligned transfer regions are selected. For DeepSeek V4 PP prefill, a producer PP worker can legitimately have no local blocks for a global KV group that appears on the decode side, so the global check can fail early with P num blocks less than D even though that worker should only transfer the groups owned by its aligned region.

Changes:

• Defer local blocks < remote blocks validation from the global group pass to the selected transfer-region path.
• For multi-group alias-aligned regions, skip remote-only groups that the current producer worker does not own.
• Keep region-level validation and add summarized group diagnostics if a real mismatch remains.

Validation:

• python3 -m py_compile vllm/distributed/kv_transfer/kv_connector/v1/mooncake/mooncake_connector.py
• Ran DeepSeek V4 full PD setup with Mooncake proxy: prefill/decode ready and scripts/send_request.sh 9000 returned HTTP 200.
• Checked dev0/dev1/dev2/dev3 logs: no P num blocks less than D, local blocks < remote blocks, or pulling kv_caches failed after the fix.

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