Fixed bugs in JetMoE models.

[Phoenix-Shen]

What does this PR do?

Fixes issue #31791.

1. Fixed bugs in JetMoE casual language model and sequence classification model.
2. The original code will report errors when we want to output the aux_loss, like described in the issue.
3. I have modified JetMoeForCausalLM and JetMoeForSequenceClassification, now they work properly and output aux_loss,
4. Meanwhile I have followed MoeCausalLMOutputWithPast class to write a new class named MoESequenceClassifierOutputWithPast to store the results of JetMoeForSequenceClassification model.
5. The code have passed the test of tests/models/jetmoe/test_modeling_jetmoe.py.

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,
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• Was this discussed/approved via a Github issue or the forum? Please add a link
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• Did you make sure to update the documentation with your changes? Here are the
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  here are tips on formatting docstrings.
• Did you write any new necessary tests?

Who can review?

@ArthurZucker

[Phoenix-Shen]

ci/circleci: tests_torch_and_tf error doesn't seem to be a problem with the code I submitted.

[yikangshen]

The check_code_quality error can be fixed with this command:
ruff format src/transformers/models/jetmoe/modeling_jetmoe.py.
The tests_torch_and_tf will usually be automatically fixed after a resubmission.

[Phoenix-Shen]

The check_code_quality error can be fixed with this command: ruff format src/transformers/models/jetmoe/modeling_jetmoe.py. The tests_torch_and_tf will usually be automatically fixed after a resubmission.

Thanks a lot, I have already formatted the files under your guidance.

[ArthurZucker]

Thanks for updating! This LGTM, let's add a test the tests the loss computation with output router logits to make sure this is properly tested!

[HuggingFaceDocBuilderDev]

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