[Quantization] Rename mxfp4 quant layer and oracle to gpt_oss_mxfp4

[zyongye]

Rename the GPT-OSS-specific MXFP4 quantization files and classes to make ownership explicit:

• oracle/mxfp4.py → oracle/gpt_oss_mxfp4.py; Mxfp4MoeBackend → GptOssMxfp4MoeBackend
• quantization/mxfp4.py → quantization/gpt_oss_mxfp4.py; Mxfp4Config → GptOssMxfp4Config, Mxfp4MoEMethod → GptOssMxfp4MoEMethod
• get_name() now returns "gpt_oss_mxfp4"; registry keeps "mxfp4" alias for backward compat with existing model JSON configs
• Update all importers (compressed_tensors_moe, quark_moe, init, layer.py, gpt_oss.py)

Kernel class names are unchanged.

Purpose

Test Plan

GPT-OSS-12OB gpqa with reasoning effort low

Test Result

test passed

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[gemini-code-assist]

Code Review

This pull request renames and namespaces the mxfp4 quantization components to gpt_oss_mxfp4 across the model executor and quantization layers. Key changes include renaming the Mxfp4MoeBackend enum to GptOssMxfp4MoeBackend, updating the quantization configuration and method classes to use the gpt_oss_mxfp4 prefix, and adjusting the gpt_oss model implementation to recognize the new quantization name. I have no feedback to provide.