Speed up device-to-host staging reads (#22023)

[SS-JIA]

Summary:

Prefer host-cached memory for device-to-host staging while preserving coherent memory preference for host-to-device staging. Invalidate only bytes consumed by readback, avoiding cache maintenance over padded staging capacity. This fixes slow Mali output copies while retaining Adreno memory selection.

Authored with Codex.

Differential Revision: D116964600

[pytorch-bot]

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🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/22023

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✅ You can merge normally! (6 Unrelated Failures)

As of commit 05de591 with merge base 90f88b7 ():

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

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

• pull / unittest / linux / linux-job (gh) (trunk failure)
  .ci/scripts/tests/test_filter_cuda_matrix.py::TestPublishedSets::test_published_python_versions
• pull / unittest / macos / macos-job (gh) (trunk failure)
  .ci/scripts/tests/test_filter_cuda_matrix.py::TestPublishedSets::test_published_python_versions
• pull / unittest / windows / windows-job (gh) (trunk failure)
  .ci/scripts/tests/test_filter_cuda_matrix.py::TestPublishedSets::test_published_python_versions
• pull / unittest-editable / linux / linux-job (gh) (trunk failure)
  .ci/scripts/tests/test_filter_cuda_matrix.py::TestPublishedSets::test_published_python_versions
• pull / unittest-editable / macos / macos-job (gh) (trunk failure)
  .ci/scripts/tests/test_filter_cuda_matrix.py::TestPublishedSets::test_published_python_versions
• pull / unittest-editable / windows / windows-job (gh) (trunk failure)
  .ci/scripts/tests/test_filter_cuda_matrix.py::TestPublishedSets::test_published_python_versions

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[meta-codesync]

@SS-JIA has exported this pull request. If you are a Meta employee, you can view the originating Diff in D116964600.

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