Feature Improvement: Automatically download and load MetaCLIP checkpoints

[Andy-LZH]

Feature Improvement based on Issue #26

Code modified/added

• src/open_clip/pretrained.py
• tests/test.py

Now loading MetaCLIP(ViT-B-32, ViT-B32-quickgelu, ViT-B-16, ViT-L-14) can be done as:

# Load MetaCLIP B32 400M
model, _, preprocess = open_clip.create_model_and_transforms('ViT-B-32-quickgelu', pretrained='metaclip400m')

# Load MetaCLIP B32 2.5B
model, _, preprocess = open_clip.create_model_and_transforms('ViT-B-32-quickgelu', pretrained='metaclip2_5b')

And thanks for reviewing this PR in advance.

[howardhsu]

thanks for naming suggestions.

[howardhsu]

all MetaCLIP are trained on quickgelu; let's NOT use nn.gelu explicitly.