[ET Device Support] CudaAllocator: device memory allocator for CUDA backend

[Gasoonjia]

Stack from ghstack (oldest at bottom):

• [ET Device Support] Add device tensor helper functions to TensorPtr API #18761
• [ET Device Support] make device support config method-based #19582
• [ET Device Support] Add ExecutorchBackendConfig flags for skipping H2D/D2H copies #18760
• [ET Device Support] PropagateDevicePass inserts H2D/D2H copy ops at delegate boundaries #18730
• [ET Device Support] Define et_copy runtime h2d and d2h copy ops #18729
• [ET Device Support] Define AOT device copy ops registry #18728
• -> [ET Device Support] CudaAllocator: device memory allocator for CUDA backend #18477
• [ET Device Support] Module: allocate device memory for planned buffers #18476

Implement CudaAllocator, a concrete DeviceAllocator using cudaMalloc/ cudaFree/cudaMemcpy for CUDA device memory management. The allocator is automatically registered with the DeviceAllocatorRegistry when the CUDA backend library is linked, ensuring DeviceMemoryBuffer::create(CUDA) works transparently.

Differential Revision: D98014184

[pytorch-bot]

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❌ 3 New Failures, 1 Pending, 6 Unrelated Failures, 1 Unclassified Failure

As of commit f21f0b2 with merge base a83e7c4 ():

NEW FAILURES - The following jobs have failed:

• Test CUDA Windows Export and E2E / export-model-cuda-windows-artifact (mistralai, Voxtral-Mini-3B-2507, non-quantized) / linux-job (gh)
  AttributeError: '_OpNamespace' 'llama' object has no attribute 'sdpa_with_kv_cache'
• Test CUDA Windows Export and E2E / export-model-cuda-windows-artifact (mistralai, Voxtral-Mini-3B-2507, quantized-int4-weight-only) / linux-job (gh)
  AttributeError: '_OpNamespace' 'llama' object has no attribute 'sdpa_with_kv_cache'
• Test CUDA Windows Export and E2E / export-model-cuda-windows-artifact (mistralai, Voxtral-Mini-4B-Realtime-2602, quantized-int4-tile... / linux-job (gh)
  AttributeError: '_OpNamespace' 'llama' object has no attribute 'sdpa_with_kv_cache'

UNCLASSIFIED FAILURE - DrCI could not classify the following job because the workflow did not run on the merge base. The failure may be pre-existing on trunk or introduced by this PR:

• Check Labels / Check labels (gh) (this job did not run on the merge base, so DrCI cannot tell whether the failure is pre-existing)
  RuntimeError: GraphQL query

FLAKY - The following job failed but was likely due to flakiness present on trunk:

• trunk / unittest-release / macos / macos-job (gh) (similar failure)
  ##[error]The operation was canceled.

BROKEN TRUNK - The following jobs failed but was present on the merge base:

👉 Rebase onto the `viable/strict` branch to avoid these failures

• pull / test-parakeet-xnnpack-linux / linux-job (gh) (trunk failure)
• pull / unittest / macos / macos-job (gh) (trunk failure)
  ##[error]The operation was canceled.
• pull / unittest-editable / macos / macos-job (gh) (trunk failure)
  ##[error]The operation was canceled.
• Test Metal Backend / test-model-metal-e2e (nvidia, parakeet-tdt, non-quantized) / macos-job (gh) (trunk failure)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 1
• Test Metal Backend / test-model-metal-e2e (nvidia, parakeet-tdt, quantized-int4-metal) / macos-job (gh) (trunk failure)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 1

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[digantdesai]

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[JacobSzwejbka]

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