Zephyr: Expand samples and documentation

[rascani]

The zephyr/ subfolder already provides external module integration (module.yml, CMakeLists.txt, Kconfig, submanifest) with a basic add model example running on Corstone 300/320 FVP (Ethos-U55/U85), Cortex-M55 CPU-only, and STM Nucleo n657x0_q. This issue extends that foundation with additional sample applications and improved documentation.

• At least 2 additional sample apps beyond the existing add model (e.g., KWS, MV2)
• Samples build with standard west build workflow
• Samples validated on >= 2 board targets (FVP + at least one hardware board)
• Documentation added to ExecuTorch docs covering the new samples
• CI validation of Zephyr samples
• Blog post announcing Zephyr support & documentation
• Stretch/P1 goal: Would be fun to have an example running 2 different models in parallel showing zephyrOS task/switches. On hardware with NPU one could use the NPU and the other stay on the CPU.

cc @psiddh @AdrianLundell @digantdesai

[zingo]

Streach/P1 goal: Would be fun to have an example running 2 different models in parallel showing zephyrOS task/switches. On hardware with NPU one could use tyhe NPU and the other stay on the CPU.

[rascani]

Streach/P1 goal: Would be fun to have an example running 2 different models in parallel showing zephyrOS task/switches. On hardware with NPU one could use tyhe NPU and the other stay on the CPU.

Thanks @zingo, great suggestion. I added it to the task list.

[zingo]

I have a bundleIO example with mv2 that is on its way. It will add kconfig settings to point out model.py and run aot_arm_compiler to lower it as a nice addon.

[cbilgin]

@psiddh, let's get a review on what landed and what's remaining and the set of PRs associated with the work.