[Core] introduce _no_split_modules to `ModelMixin` (#6396)
* introduce _no_split_modules.
* unnecessary spaces.
* remove unnecessary kwargs and style
* fix: accelerate imports.
* change to _determine_device_map
* add the blocks that have residual connections.
* add: CrossAttnUpBlock2D
* add: testin
* style
* line-spaces
* quality
* add disk offload test without safetensors.
* checking disk offloading percentages.
* change model split
* add: utility for checking multi-gpu requirement.
* model parallelism test
* splits.
* splits.
* splits
* splits.
* splits.
* splits.
* offload folder to test_disk_offload_with_safetensors
* add _no_split_modules
* fix-copies
