Improve CoreML logging with env variables

[metascroy]

Allow overriding CoreML logging level with environment variables.

[pytorch-bot]

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❌ 1 New Failure

As of commit 798aef5 with merge base 574e109 ():

NEW FAILURE - The following job has failed:

• pull / unittest-editable / macos / macos-job (gh)
  backends/xnnpack/test/ops/test_conv1d.py::TestConv1d::test_qs8_conv1d_batchnorm_seq

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@metascroy has imported this pull request. If you are a Meta employee, you can view this in D79210883.

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[facebook-github-bot]

@metascroy has imported this pull request. If you are a Meta employee, you can view this in D79210883.