[slimtensor] Add CUDA Storage with DeviceTraits and memory allocation

[Gasoonjia]

Stack from ghstack (oldest at bottom):

• rename slimtensor fiies to consistent with executorch files #16469
• [slimtensor] Add utility functions to common_shims_slim #16457
• [slimtensor] Add storage and device property getters to common_shims_slim #16455
• [slimtensor] Add common_shims_slim with basic property getters #16454
• [slimtensor] Add aoti_torch_item_bool for SlimTensor #16453
• [slimtensor] Add aoti_torch_assign_tensors_out for SlimTensor #16452
• [slimtensor] Add aoti_torch_copy_ for SlimTensor #16451
• [slimtensor] Add aoti_torch__reinterpret_tensor for SlimTensor #16450
• [slimtensor] Add aoti_torch_new_tensor_handle for SlimTensor #16449
• [slimtensor] Add aoti_torch_delete_tensor_object for SlimTensor #16448
• [slimtensor] Add SlimTensor-based aoti_torch_empty_strided #16447
• [slimtensor] Add SlimTensor-based aoti_torch_create_tensor_from_blob_v2 #16446
• [slimtensor] Add item() methods with CUDA and CPU support for scalar value extraction #16445
• [slimtensor] Add permute() and reshape() view operations #16444
• [slimtensor] Add as_strided() view operation for tensor reinterpretation #16443
• [slimtensor] Add from_blob() factory function for wrapping external memory #16442
• [slimtensor] Add non-owning storage mode for wrapping external memory #16441
• [slimtensor] Enable CUDA tensor copy #16440
• [slimtensor] Add CUDA slimtensor creation with basic functionality #16439
• -> [slimtensor] Add CUDA Storage with DeviceTraits and memory allocation #16438
• [slimtensor] Add CUDA DeviceType and extend Device class #16437
• [slimtensor] Add all required dtype support (Int8/16/32/64, Bool, BFloat16) #16399
• [slimtensor] Add factory functions for creating empty CPU tensors #16398
• [slimtensor] Add SlimTensor class with basic properties and CPU copy operation #16385
• [slimtensor] Add SizesAndStrides and dimension utility functions for slimtensor usage #16384
• [slimtensor] Storage and SharedPtr for CPU owning mode #16383
• [slimtensor] Introduce Device and ScalarType headers for SlimTensor minimal support #16382

This diff adds CUDA storage infrastructure to SlimTensor, enabling GPU memory allocation and management.

Key changes:

1. cuda/Guard.h - CUDAGuard RAII class:

   • Saves current CUDA device on construction, restores on destruction
   • Exception-safe device context switching
   • Constructors accept device index or Device object

2. core/Storage.h - Extended for CUDA support:

   • Added DeviceTraits<DeviceType::CUDA> specialization with:
     • allocate() - Uses cudaMalloc with CUDAGuard for device selection
     • free() - Uses cudaFree with warning on error
     • memcpy() - Supports Host↔Device and Device↔Device copies
   • Added DEFAULT_CUDA_DEVICE constant
   • Updated MaybeOwningStorage constructor to handle CUDA devices
   • Stub implementation when CUDA_AVAILABLE is not defined (throws error)

Differential Revision: D89826553

[pytorch-bot]

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❌ 3 New Failures, 1 Unrelated Failure

As of commit d7c581e with merge base fd6fa87 ():

NEW FAILURES - The following jobs have failed:

• pull / test-samsung-models-linux / linux-job (gh)
  RuntimeError: Command docker exec -t 1d4a1f3a569e47afc252f4a241af853aebf23228918d0ef26747f4633040096e /exec failed with exit code 1
• pull / test-samsung-quantmodels-linux / linux-job (gh)
  RuntimeError: Command docker exec -t 734eee748e347c60bedde8eccc232bae865801fda677948904c933cb3cf6df17 /exec failed with exit code 1
• Test CUDA Builds / test-model-cuda-e2e (mistralai, Voxtral-Mini-3B-2507, quantized-int4-tile-packed) / linux-job (gh)
  RuntimeError: Command docker exec -t add08cb9c4a9c78b6c565ec8cbe9dc1a3b841d02146f5c3d40cb79661d5427b4 /exec failed with exit code 1

UNSTABLE - The following job is marked as unstable, possibly due to flakiness on trunk:

• pull / android / run-emulator (gh) (#16137)
  Timeout waiting for emulator to boot.

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