Add sequence classification support for small Gemma 3 text models

[abdokaseb]

What does this PR do?

Add Gemma3TextForSequenceClassification for Gemma3 small text models following generic practice

Testing:

• Tested with single-node option, loss curve and AUC are all expected with no issue.
• All testes passed
• make fixup passed

Fixes #40554

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you read the contributor guideline,
  Pull Request section?
• Was this discussed/approved via a Github issue or the forum? Please add a link
  to it if that's the case.
• Did you make sure to update the documentation with your changes? Here are the
  documentation guidelines, and
  here are tips on formatting docstrings.
• Did you write any new necessary tests?

Who can review?

@ArthurZucker

[zucchini-nlp]

Hey @abdokaseb , thanks for the PR! Indeed, models saved without an image tower can't be loaded with existing class, totally forgot about them

[zucchini-nlp]

Failing tests are not related, a rebase might help. I will merge a PR to fix processor tests in an hour or so

[HuggingFaceDocBuilderDev]

The docs for this PR live here. All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

[zucchini-nlp]

@abdokaseb, the workers are crashing and thus we can't merge the PR yet. I will check what is wrong and merge when fixed

[github-actions]

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

run-slow: auto, gemma3

[zucchini-nlp]

The CI is very flaky lately 😿

[adamreichold]

The CI is very flaky lately 😿

@zucchini-nlp @abdokaseb Thank you for carrying it over the finish line nevertheless!

[ArthurZucker]

🤗