perf(rocm): add prepared MoE execution boundary

[JohnQinAMD]

Summary

Add an optional backend-neutral prepared-MoE boundary to MoERunner and use it
from AMD Kimi-K3 to hand route metadata to AITER exactly once.

This PR is stacked on #9 and requires the matching prepared
MoE support in JohnQinAMD/aiter-amd#22.

Design

• Define small protocols for opaque route metadata and synchronous
  prepare/consume ownership.
• Add an optional runner backend with exact fallback to the existing route and
  expert path.
• Bypass preparation when EPLB is active, preserving existing EPLB behavior.
• Translate Kimi-K3 layer, routing, and quantization state in one ROCm-specific
  AITER adapter.
• Record the AITER MXFP4 layout at weight-processing time rather than inferring
  it from model names.

Only the AMD Kimi-K3 model installs the adapter. NVIDIA model and kernel files
are unchanged. The current-main port also makes the metadata protocol
read-only and keeps backend narrowing explicit so Python 3.10 mypy validates
the ownership contract.

Performance

Kimi-K3 TP8, batch 1, 8K input / 1K output, no speculative decoding on 8x
MI355X:

Run	Decode	Mean TPOT	P50 ITL
1	69.7324 tok/s	14.3405 ms	14.3271 ms
2	69.8257 tok/s	14.3214 ms	14.3084 ms

Mean decode is 69.7791 tok/s, 8.56% above the hash-pinned 64.2744 tok/s parent.
The separately rebuilt signed commits reproduced 69.6387 tok/s mean, within
0.21% of the accuracy-tested image.

Accuracy and validation

• Frozen GSM8K: 1,256/1,319 (0.952237), one invalid response.
• Parent: 1,244/1,319 (0.943139), two invalid responses; paired outcomes were
  32 candidate wins and 20 losses.
• Focused vLLM tests in the pinned image: 4 passed.
• Matching AITER correctness: 20/20 cases and 1,000 graph replays.
• Current-main changed-file pre-commit passed, including Ruff, format, Python
  3.10 mypy, SPDX, import guards, configuration checks, and CUDA API guard.
• git diff --check passed.

Disclosure

Developed with assistance from OpenAI Codex. The author reviewed the code,
tests, numerical thresholds, and benchmark evidence.

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