Add tests for PyTorch models

[ScottTodd]

Related issues:

• Add tests for PyTorch operators #17
• Add tests for ONNX models  #6
• Add tests for TFLite models #5

I want to delete these old tests: https://github.com/nod-ai/SHARK-TestSuite/tree/main/iree_tests/pytorch/models, but want a replacement first. There are currently just two tests there, opt-125M and resnet50, each imported from "e2eshark" using this script. The e2eshark code exports using iree-turbine with the code in tools/stubs/turbinemodel.py and these test cases: resnet50/model.py, opt-125M/model.py.

I've started work on this on a branch: https://github.com/ScottTodd/iree-test-suites/tree/pytorch-models-setup. Some observations:

• Pretrained PyTorch models are available from multiple sources. Most bottom out at nn.Module, but there doesn't appear to be a convenient way to reflect on an arbitrary nn.Module to get a canonical input signature (like with ONNX).

• PyTorch models can be very flexible. It may be worth testing mutliple versions of each model: different data types, different implementations (e.g. attention op variants, different dynamic shape sizes, etc.)

• iree-turbine may have some issues on Windows:

  tests/torchvision/resnet_test.py::test_resnet50 Windows fatal exception: access violation
  
  Current thread 0x00003e6c (most recent call first):
    File "D:\dev\projects\iree-test-suites\pytorch_models\.venv\Lib\site-packages\iree\turbine\aot\support\ir_utils.py", line 332 in create_tensor_global
    File "D:\dev\projects\iree-test-suites\pytorch_models\.venv\Lib\site-packages\iree\turbine\aot\support\procedural\globals.py", line 126 in track
    File "D:\dev\projects\iree-test-suites\pytorch_models\.venv\Lib\site-packages\iree\turbine\aot\support\procedural\exported_program.py", line 323 in _lift_tensor_to_global
    ...
  

• Might first focus on export -> compile coverage, then later add runtime execution and comparison with native torch on CPU and other backends

[ScottTodd]

• iree-turbine may have some issues on Windows:

  tests/torchvision/resnet_test.py::test_resnet50 Windows fatal exception: access violation
  
  Current thread 0x00003e6c (most recent call first):
    File "D:\dev\projects\iree-test-suites\pytorch_models\.venv\Lib\site-packages\iree\turbine\aot\support\ir_utils.py", line 332 in create_tensor_global
    File "D:\dev\projects\iree-test-suites\pytorch_models\.venv\Lib\site-packages\iree\turbine\aot\support\procedural\globals.py", line 126 in track
    File "D:\dev\projects\iree-test-suites\pytorch_models\.venv\Lib\site-packages\iree\turbine\aot\support\procedural\exported_program.py", line 323 in _lift_tensor_to_global
    ...
  

FWIW, that test segfaults on Linux too, so some issues with my test setup.