[Refactor] Better align `from_single_file` logic with `from_pretrained` (#7496)
* refactor unet single file loading a bit.
* retrieve the unet from create_diffusers_unet_model_from_ldm
* update
* update
* updae
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* tests
* update
* update
* update
* Update docs/source/en/api/single_file.md
Co-authored-by: Sayak Paul <spsayakpaul@gmail.com>
* Update docs/source/en/api/single_file.md
Co-authored-by: Sayak Paul <spsayakpaul@gmail.com>
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* Update docs/source/en/api/loaders/single_file.md
Co-authored-by: YiYi Xu <yixu310@gmail.com>
* Update src/diffusers/loaders/single_file.py
Co-authored-by: YiYi Xu <yixu310@gmail.com>
* Update docs/source/en/api/loaders/single_file.md
Co-authored-by: Sayak Paul <spsayakpaul@gmail.com>
* Update docs/source/en/api/loaders/single_file.md
Co-authored-by: Sayak Paul <spsayakpaul@gmail.com>
* Update docs/source/en/api/loaders/single_file.md
Co-authored-by: Sayak Paul <spsayakpaul@gmail.com>
* Update docs/source/en/api/loaders/single_file.md
Co-authored-by: Sayak Paul <spsayakpaul@gmail.com>
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
* update
---------
Co-authored-by: sayakpaul <spsayakpaul@gmail.com>
Co-authored-by: YiYi Xu <yixu310@gmail.com>