Fixes detection of CuPy installed with pre-built wheels (#1965)

The CuPy library ships both a source distribution (`cupy`) as well as versions containing pre-built wheels (`cupy-cuda11x`, `cupy-cuda12x`, `cupy-rocm-5-0`, `cupy-rocm-4-3`). Use of `_is_package_available` to detect CuPy only works for the source distribution of CuPy and fails when using the pre-built wheels versions.

This is because the `_is_package_available` will always attempt to resolve version information (even if it's not required) and in doing so assumes that the _importable_ package name matches the _installed_ distribution name. While this is usually the case, it doesn't work for CuPy and several other libraries. ONNX Runtime for example might be installed as `onnxruntime` or `onnxruntime-gpu` and thus Optimum just uses `importlib.util.find_spec` to work around the same problem. This commit replicates the same solution for CuPy.

optimum/onnxruntime/utils.py

@@ -13,6 +13,7 @@
 #  limitations under the License.
 """Utility functions, classes and constants for ONNX Runtime."""
 
+import importlib
 import os
 import re
 from enum import Enum
@@ -31,7 +32,6 @@
 import onnxruntime as ort
 
 from ..exporters.onnx import OnnxConfig, OnnxConfigWithLoss
-from ..utils.import_utils import _is_package_available
 
 
 if TYPE_CHECKING:
@@ -91,9 +91,11 @@ def is_onnxruntime_training_available():
 
 def is_cupy_available():
     """
-    Checks if onnxruntime-training is available.
+    Checks if CuPy is available.
     """
-    return _is_package_available("cupy")
+    # Don't use _is_package_available as it doesn't work with CuPy installed
+    # with `cupy-cuda*` and `cupy-rocm-*` package name (prebuilt wheels).
+    return importlib.util.find_spec("cupy") is not None
 
 
 class ORTConfigManager: