Guard nvFuser-based tests with minimum required compute capability or BF16 capability

Running `thunder/tests/test_torch_compile_executor.py::test_torch_compile_cat_nvfuser_phi2_tanh` and likely other tests would fail on pre-Ampere GPUs with

```py
RuntimeError: Target compute capability is 7.0 but this fusion requires at least 8.0. Reason: Fusion contains BFloat16 values which was introduced in Ampere (8.0)
```
PyTorch has a utility function to query whether the current device supports BF16 `torch.cuda.is_bf16_supported`.

cc @borda @tfogal

Start in thunder/tests/test_torch_compile_executor.py with test_torch_compile_cat_nvfuser_phi2_tanh, then review nearby nvFuser-based tests. Check torch.cuda.is_bf16_supported and the existing test behavior on pre-Ampere GPUs. Done means unsupported devices no longer fail these tests while supported devices still run them.

Written by the indexing model from the issue text.