(feat)(fix) Fix Qwen quantization parsing and add Qwen 3.5 model config tests

[YouNeedCryDear]

What this PR does

• Fixes quantization config parsing for Qwen model configurations.
• Adds Qwen 3.5 model config parsing support and fixtures.
• Expands unit test coverage across Qwen parser variants, including FP8 cases.

Why we need it

Current parsing for newer Qwen model quantization config is incomplete/inaccurate in some cases, which can lead to incorrect model metadata extraction. These updates improve correctness and add regression coverage.

Fixes #

How to test

• go test ./pkg/hfutil/modelconfig/...

Checklist

• Tests added/updated (if applicable)
• Docs updated (if applicable)
• make test passes locally

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