fix: add clear error message when mistral-common is missing for AutoTokenizer loading Voxtral
Author: junjunjd
Pull request: yes

- Add clear error message when mistral-common is missing for AutoTokenizer loading Voxtral
- Add unit test

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Fixes # (issue)


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Comments:
**[For maintainers]** Suggested jobs to run (before merge)

run-slow: auto, voxtral

cc @vasqu we have quite a few PRs for this now and should probably merge one! This one seems clean, but #41592 has been open for longer

Sorry about that one, imo we should prioritize #41592, left a comment there

This PR will only work for voxtral, we should make this as general as possible as in the other PR

Hi @Rocketknight1 @vasqu . I've worked on @vasqu  suggestion and did changes .My PR #41592 passes all tests. One test (build_pr_documentation) is pending and rest are all clear.