Fix wrong param types, docs, and handles noise=None in scale_noise of FlowMatching schedulers

[Promisery]

What does this PR do?

In the scale_noise functions of all flow matching schedulers, the definitions and docs are wrong:

• timestep should be a torch.FloatTensor, not a float or int
• noise is not included in the document

Also, noise should be a required arg

Before submitting

• [x] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
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• [x] 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?

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[HuggingFaceDocBuilderDev]

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