fix: support loading .pth models

[deependujha]

Before submitting

• Was this discussed/agreed via a Github issue? (no need for typos and docs improvements)
• Did you read the contributor guideline, Pull Request section?
• Did you make sure to update the docs?
• Did you write any new necessary tests?

What does this PR do?

The README documents saving and loading PyTorch models, but .pth artifacts currently fail with NotImplementedError during loading.

import litmodels as lm
import torch

# save a model
model = torch.nn.Module()
lm.save_model(model=model, name="model-name")

# load a model
model = lm.load_model(name="model-name")

output:

File "/teamspace/studios/this_studio/LitModels/src/litmodels/io/gateway.py", line 183, in load_model
    raise NotImplementedError(f"Loading model from {model_path.suffix} is not supported yet.")
NotImplementedError: Loading model from .pth is not supported yet.

Use torch.load(..., weights_only=False) to support loading .pth artifacts containing serialized model objects and ensure the README's save/load example works as documented.

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Additional details and impacted files

@@         Coverage Diff         @@
##           main   #165   +/-   ##
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- Coverage    84%    84%   -0%     
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  Files        12     12           
  Lines       511    513    +2     
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  Hits        430    430           
- Misses       81     83    +2     

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