What does this PR do?

Fixes # (issue) vanilla attention bug, vae encode dtype limitation

Adds # (feature) Add sink size control, t5 parallel cache, impr sampling

Before submitting

[x] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
[x] Did you read the contributor guideline?
[x] Did you make sure to update the documentation with your changes? E.g. record bug fixes or new features in What's New. Here are the documentation guidelines
[ ] Did you build and run the code without any errors?
[ ] Did you report the running environment (NPU type/MS version) and performance in the doc? (better record it for data loading, model inference, or training tasks)
[ ] Did you write any new necessary tests?

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