Cortex-M backend: add cortex-m0plus to the trunk e2e CI matrix

[rascani]

Summary

Extends _test_cortex_m_e2e.yml with a targets input that joins the existing model matrix to give a target × model cross product, so trunk can exercise the same suite against multiple Cortex-M variants. The trunk job opts in to ["cortex-m55", "cortex-m0plus"]; the nightly job (and any future caller that doesn't pass targets) falls back to the M55-only default and keeps its current shape.

Cortex-M0+ is the first scalar-class (Armv6-M) variant to enter CI. It exercises the pure-C CMSIS-NN kernel path (__ARM_FEATURE_DSP and __ARM_FEATURE_MVE both undefined), covering the M0+ enablement patches that fix the Armv6-M HardFault handler and the ARMCM0plus directory-case mismatch in the Cortex DFP. M0, M3, and M23 share the same Armv6-M / Armv8-M Baseline arch family and can slot into the same targets array later without further workflow changes.

Test plan

CI

Authored with Claude.

[pytorch-bot]

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❌ 1 New Failure, 2 Unclassified Failures

As of commit c0cf171 with merge base 26b4be8 ():

NEW FAILURE - The following job has failed:

• pull / test-lora-linux / linux-job (gh)
  RuntimeError: Command docker exec -t 422704dd1ce76367cd87a67255123a2ae632861fe95b91ed4dae820d9d80de26 /exec failed with exit code 1

UNCLASSIFIED FAILURES - DrCI could not classify the following jobs because the workflow did not run on the merge base. The failures may be pre-existing on trunk or introduced by this PR:

• Build Windows Wheels / pytorch/executorch / build-wheel-py3_10-cpu (gh) (this job did not run on the merge base, so DrCI cannot tell whether the failure is pre-existing)
  Process completed with exit code 1.
• Build Windows Wheels / pytorch/executorch / upload / upload-wheel-py3_10-cpu (gh) (this job did not run on the merge base, so DrCI cannot tell whether the failure is pre-existing)
  Unable to download artifact(s): Artifact not found for name: pytorch_executorch__3.10_cpu_x64

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