[Executorch] Use temp allocator for allocating scratch memory

[kimishpatel]

Stack from ghstack (oldest at bottom):

• [Executorch][LLM] Use caching allocator for runner #15730
• [Executorch] Make module constructors uniform across #15729
• -> [Executorch] Use temp allocator for allocating scratch memory #15728
• [Executorch] Introduce caching cpu memory allocator #15611
• Reduce allocation overhead in quantized sdpa #15610
• [Executorch] Add multithreading for op_quantize #15609
• [Executorch] Add simd path for op quantize #15608
• [Executorch] parallelize op_choose_qparams #15607
• [Executorch][llm] Fix flakyness of quantized sdpa test #15653

This allows us to leverage temp memory allocator and if that allocator is caching allocator it reduces the allocaiton overhead.

Differential Revision: D85532076

[pytorch-bot]

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❌ 5 New Failures, 1 Unrelated Failure

As of commit 351a400 with merge base aba44fd ():

NEW FAILURES - The following jobs have failed:

• pull / test-llama-runner-linux (fp32, xnnpack+custom+quantize_kv, linux.2xlarge, executorch-ubuntu-22.04... / linux-job (gh)
  RuntimeError: Command docker exec -t ac6dce3d3eec000fa958a65d5586141cecb8f1130b4b10abef3c866b42b1b252 /exec failed with exit code 1
• pull / unittest / linux / linux-job (gh)
  backends/xnnpack/test/recipes/test_xnnpack_recipes.py::TestXnnpackRecipes::test_int8_static_quant_recipe
• pull / unittest / macos / macos-job (gh)
  backends/xnnpack/test/recipes/test_xnnpack_recipes.py::TestXnnpackRecipes::test_int8_static_quant_recipe
• pull / unittest-editable / linux / linux-job (gh)
  backends/xnnpack/test/recipes/test_xnnpack_recipes.py::TestXnnpackRecipes::test_int8_static_quant_recipe
• pull / unittest-editable / macos / macos-job (gh)
  backends/xnnpack/test/recipes/test_xnnpack_recipes.py::TestXnnpackRecipes::test_int8_static_quant_recipe

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

• pull / test-models-linux (resnet18, portable, linux.2xlarge) / linux-job (gh) (matched linux rule in flaky-rules.json)
  Error response from daemon: Get "https://308535385114.dkr.ecr.us-east-1.amazonaws.com/v2/": net/http: request canceled while waiting for connection (Client.Timeout exceeded while awaiting headers)

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