Arm backend: Test fixes for TOSA on Arm64

[zingo]

cc @digantdesai @freddan80 @per @oscarandersson8218 @mansnils @Sebastian-Larsson @robell @rascani

[pytorch-bot]

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• [ROCm] MI350 CI jobs will have longer queue times due to CI migration

❌ 6 New Failures, 10 Pending

As of commit ad6ed3a with merge base 5f71611 ():

NEW FAILURES - The following jobs have failed:

• Cadence Build & Test / hifi-build / hifi4 (gh)
  Input required and not supplied: aws-region
• Cadence Build & Test / vision-build / vision (gh)
  Input required and not supplied: aws-region
• pull / test-llama-runner-qnn-linux (fp32, qnn_8a8w, qnn) / linux-job (gh)
  RuntimeError: Command docker exec -t e8ec9962d95784f556a2cfb85e821896543cd2afe5c13ab87e1024dddee4fd62 /exec failed with exit code 92
• pull / test-qnn-models-linux (dl3) / linux-job (gh)
  RuntimeError: Command docker exec -t b750db9cbeff2df2574b4a1641cd790ad313bcd3222b78cab34cf59bac288452 /exec failed with exit code 92
• trunk / test-qnn-model (fp32, ic4) / linux-job (gh)
  RuntimeError: Command docker exec -t f65fab822f2551180db8fa8855f3e7a96fc231a00d0e3ed0c66d3d203812f276 /exec failed with exit code 92
• trunk / test-qnn-model (fp32, vit) / linux-job (gh)
  RuntimeError: Command docker exec -t dca44fc73f3fc801d74a80795d37f6fb994d5c27e32b319618543c19e6e3480f /exec failed with exit code 92

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[Copilot]

Pull request overview

Adjusts Arm backend model tests to account for known numeric mismatches on aarch64 when running TOSA FP/BF16 paths, reducing spurious CI failures on Arm64 hosts.

Changes:

• Add an aarch64/arm64 host detection helper (common.is_aarch64_host()).
• Mark the ResNet18 TOSA BF16 test as xfail on aarch64 due to a known mismatch (MLETORCH-2048).
• Relax/xfail specific aarch64 cases for MobileNetV3 FP16 tolerance and Qwen3-VL BF16 vision patch embedding.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
backends/arm/test/common.py	Adds is_aarch64_host() helper for host-conditional test behavior.
backends/arm/test/models/test_resnet18.py	Xfails ResNet18 TOSA BF16 on aarch64 for known mismatch.
backends/arm/test/models/test_mobilenet_v3_arm.py	Adjusts FP16 atol on aarch64 (and adds a clarifying comment).
backends/arm/test/models/Qwen3_VL/test_qwen3_vl_layers.py	Adds per-case xfail for BF16 vision_patch_embed on aarch64.

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Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated no new comments.