Refine Apple API usage in README

[pytorchbot]

Updated input tensor creation and module forward calls in Swift and C++ examples.

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/15122

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❌ 1 New Failure, 3 Cancelled Jobs

As of commit 04134b3 with merge base e0dda90 ():

NEW FAILURE - The following job has failed:

• Build Presets / apple (llm) / build (gh)
  The process '/opt/homebrew/bin/git' failed with exit code 1

CANCELLED JOBS - The following jobs were cancelled. Please retry:

• pull / test-llava-runner-linux / linux-job (gh)
  ##[error]The operation was canceled.
• pull / unittest / macos / macos-job (gh)
  ##[error]The operation was canceled.
• pull / unittest-editable / macos / macos-job (gh)
  ##[error]The operation was canceled.

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