[Qwen3ASR] Add hotword parsing, and fix language parsing and training.
Author: ebezzam
Pull request: yes

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# What does this PR do?

A few patches for Qwen3 ASR:
- add support for custom hotwords, e.g. passing custom vocabulary to help transcription like [VibeVoice](https://huggingface.co/microsoft/VibeVoice-ASR-HF#providing-context). Original [model card](https://huggingface.co/Qwen/Qwen3-ASR-1.7B) and [repo](https://github.com/QwenLM/Qwen3-ASR) didn't show such examples... but a user [comment](https://huggingface.co/Qwen/Qwen3-ASR-0.6B-hf/discussions/2) on the new checkpoints brought up this feature not handled by current code. And looking into original code, I see this context [arg](https://github.com/QwenLM/Qwen3-ASR/blob/7c6daf77a2421100f5fb066495372c00129d39ff/qwen_asr/inference/qwen3_asr.py#L303).
- language hint should be handled differently
- while doing above, I noticed a training bug which was copied from other models, because AudioFlamingo3, GlmASR, and MusicFlamingo were affected by [this refactor](https://github.com/huggingface/transformers/pull/45493) (I'll open a separate PR to fix them)

Comments:
The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_47111). All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

run-slow: qwen3_asr

[Workflow Run ⚙️](https://github.com/huggingface/transformers/actions/runs/28802105094)

This comment contains `run-slow`, running the specified jobs: 

models: ["models/qwen3_asr"]
quantizations: []

## CI Results
[Workflow Run ⚙️](https://github.com/huggingface/transformers/actions/runs/28802105094)

### Commit Info
| Context | Commit | Description |
|---------|--------|-------------|
| RUN | [d167b695](https://github.com/huggingface/transformers/commit/d167b69558710ebc8355b159f8ef5fdbb4f7e228) | workflow commit (merge commit) |
| PR | [e4cf30a3](https://github.com/ebezzam/transformers/commit/e4cf30a3e87bd3a93e21d556770d0f62845c821a) | branch commit (from PR) |
| main | [1da9d1d4](https://github.com/huggingface/transformers/commit/1da9d1d433c301f59027668b25f42d317ec742df) | base commit (on `main`) |

✅ No failing test specific to this PR 🎉 👏 !


run-slow: qwen3_asr

[Workflow Run ⚙️](https://github.com/huggingface/transformers/actions/runs/28885159623)

This comment contains `run-slow`, running the specified jobs: 

models: ["models/qwen3_asr"]
quantizations: []

## CI Results
[Workflow Run ⚙️](https://github.com/huggingface/transformers/actions/runs/28885159623)

### Commit Info
| Context | Commit | Description |
|---------|--------|-------------|
| RUN | [b5cbed78](https://github.com/huggingface/transformers/commit/b5cbed782efa0f53a813f8cf7e2345b75ca0b19d) | workflow commit (merge commit) |
| PR | [caf37300](https://github.com/ebezzam/transformers/commit/caf37300fc3d3333c3d7c2162a92a886e424eb1c) | branch commit (from PR) |
| main | [4af901d5](https://github.com/huggingface/transformers/commit/4af901d5ed20e86d311e64013bfe3d2dbec0eff7) | base commit (on `main`) |

✅ No failing test specific to this PR 🎉 👏 !


**[For maintainers]** Suggested jobs to run (before merge)

run-slow: musicflamingo, qwen3_asr, vibevoice_asr

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---

### CI recap

**Dashboard:** [View test results in Grafana](https://transformers-ci.lor-e.huggingface.cool/d/pytest-observability-by-pr/pytest-observability-branch?var-pr=47111)
**Latest run:** [29020934031:1](https://github.com/huggingface/transformers/actions/runs/29020934031)
**Result:** `failure` | **Jobs:** 12 | **Tests:** 169,853 | **Failures:** 2 | **Duration:** 16h 51m

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