Safetensor loading in AnimateDiff conversion scripts

[DN6]

What does this PR do?

Add support for converting safetensors format AnimateDiff checkpoints to diffusers.

Fixes # (issue) #7751

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• [ ] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
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• [ ] Did you write any new necessary tests?

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