[Core] Psutil process attr num_fds is not available on Windows

[jjyao]

Why are these changes needed?

Per psutil doc, num_fds is not available on Windows so we should exclude it when fetching process attrs.

Related issue number

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• I've run scripts/format.sh to lint the changes in this PR.
• I've included any doc changes needed for https://docs.ray.io/en/master/.
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    method in Tune, I've added it in doc/source/tune/api/ under the
    corresponding .rst file.
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• Testing Strategy
  • Unit tests
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  • This PR is not tested :(

[can-anyscale]

i enable auto-merge so we can get this in as soon as we can; it takes several hours for the automation to confirm that this test is fixed in the master branch

[can-anyscale]

actually test_metric_agent is failing on premerge @jjyao ;(

[can-anyscale]

test for windows://python/ray/tests:test_actor_state_metrics https://buildkite.com/ray-project/postmerge/builds/5181

[can-anyscale]

let's go