[II] Preserve FP32 and FP8 Kimi projection payloads

[voipmonitor]

Behavior

• Extends the Kimi-K3 B12X projection gather to FP32 and FP8 E4M3 outputs.
• Reinterprets FP32 values as one-byte transport lanes and restores FP32 after the gather; the operation performs no numerical conversion.
• Transports FP8 E4M3 directly when its local row satisfies the B12X alignment contract.
• Preserves the standard tensor-parallel all-gather fallback for unsupported dtypes or alignment.

Technical reason

The Kimi-K3 latent projection uses BF16, while the tensor-parallel router projection produces FP32 scores and online-quantized projections can produce FP8. These payloads require the same lossless decode transport without introducing a dtype conversion into routing or projection arithmetic.

Compatibility

• This pull request is stacked on [II] Gather sharded Kimi projections through B12X #346.
• No path changes unless Kimi projection sharding is active and VLLM_USE_B12X_DCP_A2A=1.
• FP16 and BF16 behavior is unchanged.
• Unsupported FP32 and FP8 widths retain the standard collective.

Validation

Executed in voipmonitor/vllm:kimi-k3-qsrt-ii-vllm735952b-b12x180ccab-cu133-torch213-20260815-r3 with the changed source files mounted over the installed tree:

pytest -q tests/models/kimi_k3/test_tp_projection.py
7 passed

The tests verify per-rank BF16 padding removal, bit-preserving FP32 transport, direct FP8 transport, coordinator selection, and exact fallback behavior. Ruff formatting, Ruff lint, and git diff --check also pass.

[coderabbitai]

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[voipmonitor]

The behavior implemented by this pull request is preserved unchanged in vLLM #385 as commit 17b9f73216cc. Stable Git patch IDs match. Review and merge #385; this pull request is closed to avoid duplicate review.