fix: rewind file pointer and handle AttributeError on JIT load fallback

[reginaldalfret]

Summary

In clip.load(), when attempting to load a checkpoint file, the function first tries torch.jit.load():

        try:
            # loading JIT archive
            model = torch.jit.load(opened_file, map_location=device if jit else "cpu").eval()
            state_dict = None
        except RuntimeError:
            ...
            state_dict = torch.load(opened_file, map_location="cpu")

If torch.jit.load() encounters an incompatibility (such as an AttributeError from missing script attributes in certain environments) or fails after reading initial bytes from the stream:

1. AttributeError was uncaught, causing an unhandled crash rather than falling back to loading a plain PyTorch state_dict.
2. The open file stream pointer was not rewound (opened_file.seek(0)), causing torch.load() to read from an offset position and fail during unpickling.

Fix

• Catch (RuntimeError, AttributeError) in the fallback handler.
• Rewind the file stream with opened_file.seek(0) before calling torch.load(opened_file).

Validation

• Added unit test tests/test_model_fallback.py verifying that when torch.jit.load raises AttributeError, clip.load catches it, rewinds the file stream, and loads the model via torch.load.
• Test passes cleanly.

Closes #494