[CI/Build] Reorganize models tests

[DarkLight1337]

• Instead of nesting by <arch/task> -> <modality>, we now nest the directories by <modality> -> <task> to better align with our test grouping in CI.
• Combine audio and vision test directories together since some models support both.
• Don't separate by architecture anymore since V1 should have built-in encoder-decoder support.
• Quantization models tests have been moved into a separate directory tests/models/quantization, removing the need for quant_model pytest mark since they can now be conveniently selected.
• Also, fix a bunch of failing model tests

[github-actions]

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[Isotr0py]

Overall LGTM. Let's add missing mixed modality for other omni models in a following PR!

[NickLucche]

V1 should have built-in encoder-decoder support

Are you referring to MM vit encoder + text decoder? Because I missed the news about good old encoder-decoder support on V1 🤔

[DarkLight1337]

V1 should have built-in encoder-decoder support

Are you referring to MM vit encoder + text decoder? Because I missed the news about good old encoder-decoder support on V1 🤔

From my understanding (correct me if I'm wrong @ywang96 ), the V1 model runner is designed to accommodate models that use cross-attention without having to define a separate encoder-decoder model runner.