fix the warning torch_dtype is deprecated

[msdsm]

Motivation

When users load pipelines like QwenImageEditPipeline with the torch_dtype parameter, they see a deprecation warning from the Transformers library. However, changing to dtype (as the warning suggests) causes errors because diffusers' from_pretrained doesn't accept dtype as a parameter.

This creates a confusing user experience where:

1. Users see a deprecation warning
2. Following the warning's advice breaks their code
3. There's no way to avoid the warning without modifying the diffusers library

Solution

This PR internally converts torch_dtype to dtype when loading Transformers models (transformers >= 4.20.0), while keeping torch_dtype for diffusers models and other components.

Fixes #12840

Who can review?

• Pipelines and pipeline callbacks: @yiyixuxu and @asomoza