Cap torchvision/torchaudio versions, remove amdhip64.dll fallback, fix visible GPU count

- Cap torchvision<0.26.0 and torchaudio<2.11.0 alongside torch<2.11.0 in
  both install.sh and install_python_stack.py to prevent resolver from
  selecting incompatible companion packages from ROCm wheel index
- Remove amdhip64.dll fallback in Windows ROCm detection (DLL presence
  without hipinfo/amd-smi is not proof of GPU existence)
- Fix get_visible_gpu_count() to use _get_parent_visible_gpu_spec() which
  respects HIP_VISIBLE_DEVICES/ROCR_VISIBLE_DEVICES on ROCm hosts

studio/install_python_stack.py

@@ -187,8 +187,8 @@ def _ensure_rocm_torch() -> None:
         "--force-reinstall",
         "--no-cache-dir",
         "torch>=2.4,<2.11.0",
-        "torchvision",
-        "torchaudio",
+        "torchvision<0.26.0",
+        "torchaudio<2.11.0",
         "--index-url",
         index_url,
         constrain = False,