Fix coreml rank0

[metascroy]

coremltools wraps rank 0 tensors as rank1 tensors in the AOT flow when producing a PTE file. This PR:

• Applies the same change on the coreml runtime
• Changes CoreML model tests to use the partitioner

Fixes #10451

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/10534

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❌ 2 New Failures, 1 Unrelated Failure

As of commit 65171cc with merge base c991de4 ():

NEW FAILURES - The following jobs have failed:

• Lint / link-check / lint-urls / linux-job (gh)
  RuntimeError: Command docker exec -t 5de5bde1184f212227d0b8b873f3dcb9b95a61ca7e98721c1bb891cd029ebf01 /exec failed with exit code 1
• pull / android / run-emulator (gh)
  The process '/usr/bin/sh' failed with exit code 255

BROKEN TRUNK - The following job failed but were present on the merge base:

👉 Rebase onto the `viable/strict` branch to avoid these failures

• trunk / test-coreml-delegate / macos-job (gh) (trunk failure)
  /Users/runner/work/executorch/executorch/pytorch/executorch/backends/apple/coreml/runtime/test/ETCoreMLModelManagerTests.mm:220:28: error: member access into incomplete type 'const value_type' (aka 'const executorchcoreml::MultiArray')

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