Add Qwen 3.5 MoE to cuda-perf CI and add prefill throughput tracking

[Gasoonjia]

• Add PyTorchObserver stats output to qwen3_5_moe runner (enables cuda_benchmark.py parsing), --prompt_file flag, and GPU memory stats
• Add prefill_throughput metric to cuda_benchmark.py (prefill tok/s alongside existing decode tok/s)
• Add Qwen3.5-35B-A3B-HQQ-INT4 to cuda-perf.yml with >1000 token prompt and 512 output tokens, on linux.aws.a100
• Align cuda-perf.yml triggers with cuda.yml (push main/release, ciflow/cuda tags, PR on backends/cuda and backends/aoti paths)
• Remove random model selection and schedule trigger; always run all models when triggered

[pytorch-bot]

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❌ 4 New Failures, 25 Pending, 1 Unrelated Failure

As of commit 7336416 with merge base 28c56fe ():

NEW FAILURES - The following jobs have failed:

• pull / android / run-emulator (gh)
  The process '/usr/local/lib/android/sdk/platform-tools/adb' failed with exit code 224
• trunk / test-torchao-huggingface-checkpoints (lfm2_5_1_2b, linux.arm64.2xlarge, executorch-ubuntu-22.04-g... / linux-job (gh)
  RuntimeError: Command docker exec -t 13ba2a762a54b4ab0b39bc45b1d34ef72d70a86eae2221ebc18c40d409573f97 /exec failed with exit code 1
• trunk / test-torchao-huggingface-checkpoints (phi_4_mini, linux.arm64.2xlarge, executorch-ubuntu-22.04-gc... / linux-job (gh)
  RuntimeError: Command docker exec -t 95b0017e20b9e4ecc6ce1faa320d2d03c396f8c4fb553657fab4f574f3df43fb /exec failed with exit code 1
• trunk / test-torchao-huggingface-checkpoints (qwen3_4b, linux.arm64.2xlarge, executorch-ubuntu-22.04-gcc1... / linux-job (gh)
  RuntimeError: Command docker exec -t b02f1d8a2b04d3331eb654ef2bc0318964344cfeb83c22c0219816b090c02b92 /exec failed with exit code 1

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

• pull / unittest-arm-backend-with-no-deps (test_pytest_ops_tosa) / linux-job (gh) (detected as infra flaky with no log or failing log classifier)

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