Make pillow a full dependency

[Mukamik]

Issue:

Pillow is listed as a package.extra, even though it seems to be explicitly depended upon even when passing images as base64 instead of PIL images.
This seems to happen because the functions that support image formats other than PIL still convert the other formats to PIL during the process (_convert_to_parts, _load_image_from_gcs, etc)

Proposal:

Convert pillow to a full dependency.

Relevant lines:

https://github.com/langchain-ai/langchain-google/blob/main/libs/genai/langchain_google_genai/chat_models.py#L209-L261

Error message:

File "/usr/local/lib/python3.12/site-packages/langchain_google_genai/chat_models.py", line 234, in _url_to_pil
  raise ImportError(
ImportError: PIL is required to load images. Please install it with `pip install pillow`

[lkuligin]

I'm not sure we want to keep PIL as a required dependency.
Have you tried to install the package with pip install langchain-google-genai[images]?

P.S. We should probably adjust the error message though. Would you be open to send a PR for that, please?

[AmgadHasan]

Yes, I think we should keep PIL as an optional dependency. It is a big package and can result in unnecessarily large file sizes.

The error message should be improved though

[lkuligin]

it looks to be stale, closing