add ascend npu accelerator support (#24879)

* Add Ascend NPU accelerator support

* fix style warining

src/transformers/testing_utils.py

@@ -91,6 +91,7 @@ from .utils import (
     is_torch_bf16_cpu_available,
     is_torch_bf16_gpu_available,
     is_torch_neuroncore_available,
+    is_torch_npu_available,
     is_torch_tensorrt_fx_available,
     is_torch_tf32_available,
     is_torch_tpu_available,
@@ -587,6 +588,26 @@ def require_torch_neuroncore(test_case):
     )
 
 
+def require_torch_npu(test_case):
+    """
+    Decorator marking a test that requires NPU (in PyTorch).
+    """
+    return unittest.skipUnless(is_torch_npu_available(), "test requires PyTorch NPU")(test_case)
+
+
+def require_torch_multi_npu(test_case):
+    """
+    Decorator marking a test that requires a multi-NPU setup (in PyTorch). These tests are skipped on a machine without
+    multiple NPUs.
+
+    To run *only* the multi_npu tests, assuming all test names contain multi_npu: $ pytest -sv ./tests -k "multi_npu"
+    """
+    if not is_torch_npu_available():
+        return unittest.skip("test requires PyTorch NPU")(test_case)
+
+    return unittest.skipUnless(torch.npu.device_count() > 1, "test requires multiple NPUs")(test_case)
+
+
 if is_torch_available():
     # Set env var CUDA_VISIBLE_DEVICES="" to force cpu-mode
     import torch