[Cria][Lllama runner] Use caching temp allocator

[kimishpatel]

Stack from ghstack (oldest at bottom):

• [Executorch] make slice_copy parallel #15830
• -> [Cria][Lllama runner] Use caching temp allocator #16081
• [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

Use of caching allocator improves TITO model performance by 6+ %.

Will add repro instructions here but requires next diff to see the impact

Differential Revision: D85532078

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/16081

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❌ 3 New Failures

As of commit 64a7cc7 with merge base 8af8252 ():

NEW FAILURES - The following jobs have failed:

• pull / android / build-llm-demo / linux-job (gh)
  /pytorch/executorch/extension/memory_allocator/cpu_caching_malloc_allocator.cpp:42:17: error: excess elements in scalar initializer
• pull / test-llama-runner-linux-android / linux-job (gh)
  /pytorch/executorch/extension/memory_allocator/cpu_caching_malloc_allocator.cpp:42:17: error: excess elements in scalar initializer
• pull / test-multimodal-linux (gemma3-4b) / linux-job (gh)
  RuntimeError: Command docker exec -t 4e95deca903b5b3b564b46a8464c07fe6214c2f5da1aa5519913206b28be3995 /exec failed with exit code 139

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