NAS-133683 / 25.04 / Refactor CPU reporting

[Qubad786]

Context

It was requested that we make some refactoring changes to our CPU reporting. Following points have been catered to:

1. /proc/stat has been disabled
2. CPU stats like user/nice etc are not being saved/retrieved
3. We were calculating the usage incorrectly which has been addressed
4. Data structure of CPU stats has been changed in realtime reporting

Example payload of what we send in realtime reporting for CPU metrics

    "cpu": {
      "cpu": {
        "usage": 33,
        "temp": null
      },
      "cpu0": {
        "usage": 100,
        "temp": null
      },
      "cpu1": {
        "usage": 1,
        "temp": null
      },
      "cpu2": {
        "usage": 0,
        "temp": null
      }
    },

[bugclerk]

Jira URL: https://ixsystems.atlassian.net/browse/NAS-133683

[yocalebo]

Looks great, thank you! Please do not merge until UI has a PR up and can adapt to these changes since this affects the dashboard widgets.

[yocalebo]

temp isn't working in my tests.

[yocalebo]

Sorry, I was wrong. This is working, re-approving (but still don't merge yet).

[RehanY147]

Hello. I am getting this response in reporting.realtime response under CPU over and over. Usage values are always 0.

{
	"cpu": {
		"cpu": {
			"usage": 0,
			"temp": null
		},
		"cpu0": {
			"usage": 0,
			"temp": null
		},
		"cpu1": {
			"usage": 0,
			"temp": null
		},
		"cpu2": {
			"usage": 0,
			"temp": null
		},
		"cpu3": {
			"usage": 0,
			"temp": null
		}
	}
}

[bugclerk]

JIRA ticket https://ixsystems.atlassian.net/browse/NAS-133683 is targeted to the following versions which have not received their corresponding PRs: 25.10

[bugclerk]

This PR has been merged and conversations have been locked.
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