[ROCm][Quantization][3/N] Refactor quark_moe w4a4 w/ oracle

[BowenBao]

Includes changes from #39136

• refactor quark_moe w4a4 to use oracle.
• all quark_moe mxfp4 configs now use oracle.
• add qwen3.5 mxfp4 w4a4 eval test to cover both aiter and emulation backend.
• updates error messages to be more actionable for oracle & aiter experts when no backend is available.

[gemini-code-assist]

Code Review

This pull request refactors and extends ROCm MXFP4 MoE support by introducing specialized AITER backends for W4A16, W4A8, and W4A4 quantization schemes. Key changes include the implementation of AiterW4A8ExpertsMonolithic using Triton kernels, the addition of AiterMxfp4Experts for W4A4, and a significant refactor of the Quark MoE method to utilize centralized oracle-based backend selection. The PR also enhances the testing suite with new oracle-based execution tests and GFX950-specific validation. Feedback is provided regarding code duplication in the reference MoE implementation and weight dequantization logic within the test suite, suggesting the extraction of these routines into helper functions to improve maintainability.

[claude]

Claude Code Review

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