Add support for Voxtral-4B-TTS-2603 to transformers

[sachinkumarsingh092]

What does this PR do?

Fixes #45027

Voxtral-4B-TTS-2503 currently does not have support for inference via transformers library and only uses vllm-omni. This PR adds that.

Paper: https://arxiv.org/abs/2603.25551v2
Huggingface card: https://huggingface.co/mistralai/Voxtral-4B-TTS-2603

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[github-actions]

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

run-slow: auto, voxtral_tts

[github-actions]

View the CircleCI Test Summary for this PR:

https://huggingface.co/spaces/transformers-community/circle-ci-viz?pr=45401&sha=bdac96

[Rocketknight1]

cc @eustlb @ebezzam