[Modular] Allow custom blocks to be saved to local_dir

[DN6]

What does this PR do?

Make it so that custom blocks can be saved to local_dir so that they are easy to edit.

Fixes # (issue)

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[DN6]

Removing this since it's not used anywhere downstream.

[HuggingFaceDocBuilderDev]

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[DN6]

cc: @yiyixuxu gentle ping

[yiyixuxu]

ohh but i thought you have a pretrained_model_name_or_path that's local, it would work already?

florence-2-custom-block is a local directory i have here

>>> from diffusers import ModularPipelineBlocks
Modular Diffusers is currently an experimental feature under active development. The API is subject to breaking changes in future releases.
>>> blocks = ModularPipelineBlocks.from_pretrained("florence-2-custom-block", trust_remote_code=True)
`trust_remote_code` is enabled. Downloading code from florence-2-custom-block. Please ensure you trust the contents of this repository
>>> blocks
Florence2ImageAnnotatorBlock {
  "_class_name": "Florence2ImageAnnotatorBlock",
  "_diffusers_version": "0.36.0.dev0"
}

[DN6]

@yiyixuxu This is for saving to a local dir from the Hub. Loading from local works currently.

[yiyixuxu]

ohh so when you do from_pretrained() it will also save to a local directory, got it

[yiyixuxu]

thanks