Improve Fake Tensor Error When Data Ptr is Accessed

[eellison]

🐛 Describe the bug

The error is not very informative as is:

The tensor has a non-zero number of elements, but its data is not allocated yet. Caffe2 uses a lazy allocation, so you will need to call mutable_data() or raw_mutable_data() to actually allocate memory.?

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[eellison]

This has been updated:

<stdin>:1: UserWarning: Accessing the data pointer of FakeTensor is deprecated and will error in PyTorch 2.5. This is almost definitely a bug in your code and will cause undefined behavior with subsystems like torch.compile. Please wrap calls to tensor.data_ptr() in an opaque custom op; If all else fails, you can guard accesses to tensor.data_ptr() on isinstance(tensor, FakeTensor). (Triggered internally at /data/users/eellison/pytorch/c10/core/StorageImpl.cpp:34.)