Address ernie-image review findings #13577 (#13663)
* Address ernie-image review findings #13577
* Use concrete Mistral3Model / Ministral3ForCausalLM types
* Cast bn_mean/bn_std to latents dtype + add TODO for hub eps
* Use VaeImageProcessor.postprocess in standard and modular ernie
* Revert "Use concrete Mistral3Model / Ministral3ForCausalLM types"
This reverts commit 2b297bf4b54deccb6cd5b82e881f29bca18259d7.
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Co-authored-by: YiYi Xu <yixu310@gmail.com>
