Arm backend: Report CPU time per inference for Ethos-U on Linux

[vacu9708]

Summary

EthosUBackend::execute() calls the EthosUBackend_execute_begin() / EthosUBackend_execute_end() hooks around each delegated inference.

• The Cortex-M runner reports the CPU time spent in EthosUBackend::execute() per inference.
• The Linux runtime runner does not.

I added a Linux branch to arm_perf_monitor.cpp to measure the CPU time saved by a Linux runtime change (#22599)

Draft

This is a draft because I'm not sure an Arm-specific measurement belongs in the portable executor_runner, though ET_ENABLE_VGF_INPUT_DUMP is a precedent.
Would this be mergeable if I only added the Linux branch to arm_perf_monitor.cpp and left out the calls in the portable executor_runner?

[pytorch-bot]

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⚠️ 22 Awaiting Approval

As of commit 503aa16 with merge base c9eee94 ():

AWAITING APPROVAL - The following workflows need approval before CI can run:

• Build Aarch64 Linux CUDA Wheels (gh)
• Build Aarch64 Linux Wheels (gh)
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