Failure to compile ONNX Kokoro-TTS model

https://huggingface.co/onnx-community/Kokoro-82M-ONNX/blob/main/onnx/model.onnx

iree-compile --iree-hal-target-device=local --iree-hal-local-target-device-backends=llvm-cpu --iree-llvmcpu-target-cpu=host kokoro_fp32.mlir -o kokoro_fp32.vmfb

```
kokoro_fp32.mlir:2137:13: error: failed to legalize operation 'torch.operator' that was explicitly marked illegal
%2133 = torch.operator "onnx.STFT"(%2131, %313, %314, %315) {torch.onnx.onesided = 1 : si64} : (!torch.vtensor<[?,?],f32>, !torch.vtensor<[],si64>, !torch.vtensor<[20],f32>, !torch.vtensor<[],si64>) -> !torch.vtensor<[],f32>
^
kokoro_fp32.mlir:2137:13: note: see current operation: %13100 = "torch.operator"(%13096, %627, %629, %631) <{name = "onnx.STFT"}> {torch.onnx.onesided = 1 : si64} : (!torch.vtensor<[?,?],f32>, !torch.vtensor<[],si64>, !torch.vtensor<[20],f32>, !torch.vtensor<[],si64>) -> !torch.vtensor<[],f32>
```

iree-compile --iree-hal-target-device=vulkan kokoro_fp32.mlir -o kokoro_fp32.vmfb

```
kokoro_fp32.mlir:2137:13: error: failed to legalize operation 'torch.operator' that was explicitly marked illegal
%2133 = torch.operator "onnx.STFT"(%2131, %313, %314, %315) {torch.onnx.onesided = 1 : si64} : (!torch.vtensor<[?,?],f32>, !torch.vtensor<[],si64>, !torch.vtensor<[20],f32>, !torch.vtensor<[],si64>) -> !torch.vtensor<[],f32>
^
kokoro_fp32.mlir:2137:13: note: see current operation: %13100 = "torch.operator"(%13096, %627, %629, %631) <{name = "onnx.STFT"}> {torch.onnx.onesided = 1 : si64} : (!torch.vtensor<[?,?],f32>, !torch.vtensor<[],si64>, !torch.vtensor<[20],f32>, !torch.vtensor<[],si64>) -> !torch.vtensor<[],f32>
```

Start with kokoro_fp32.mlir at the reported operation and compare the model at onnx/model.onnx. Investigate how iree-compile legalizes torch.operator for onnx.STFT for both the llvm-cpu and Vulkan commands; done means the model compiles without the reported legalization error.

Written by the indexing model from the issue text.