resource_manager: change cpu time unit from ms to ns

[glorv]

What problem does this PR solve?

Issue Number: Ref #5851

What is changed and how does it work?

Change the cpu time uint from ms to ns because ms is too coarse-grained that it will ignore duration small than 1ms.

Check List

Tests

• Unit test

Code changes

Side effects

• Breaking backward compatibility

Related changes

• PR to update pingcap/docs/pingcap/docs-cn:
• PR to update pingcap/tiup:
• Need to cherry-pick to the release branch

Release note

None.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• JmPotato
• nolouch

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[glorv]

/cc @nolouch @JmPotato PTAL

[ti-chi-bot]

@glorv: GitHub didn't allow me to request PR reviews from the following users: PTAL.

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/cc @nolouch @JmPotato PTAL

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[nolouch]

/merge

[ti-chi-bot]

@nolouch: It seems you want to merge this PR, I will help you trigger all the tests:

/run-all-tests

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[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: e0423ea