[Bugfix]: Use float32 for base64 embedding

[HollowMan6]

We should force the data type to be float32 as used by OpenAI Python client:
https://github.com/openai/openai-python/blob/e4a9553eaedc4fb0ada3917e867d147d03740f60/src/openai/resources/embeddings.py#L209C17-L212C1

True FIX to #6744

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[github-actions]

👋 Hi! Thank you for contributing to the vLLM project.
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[DarkLight1337]

Thanks for fixing!