metrics: fix copr-cache metrics (#26339)

[ti-srebot]

cherry-pick #26339 to release-5.0
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# In tidb repo:
git pr https://github.com/pingcap/tidb/pull/26343

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---

Signed-off-by: Shuaipeng Yu [email protected]

What problem does this PR solve?

Issue Number: close #26338

Problem Summary:
The metrics formula is wrong on Grafana.

What is changed and how it works?

Proposal: xxx

What's Changed:
Fix it as a counter.

How it Works:

Check List

Tests

• Manual test (add detailed scripts or steps below)
  The same step in the issue Copr-cache metrics on TiDB have no data #26338 .

Release note

• Fix copt-cache metrics, it will display the number of hits/miss/evict on Grafana.

[ti-srebot]

/run-all-tests

[ti-srebot]

@jackysp you're already a collaborator in bot's repo.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• XuHuaiyu
• jackysp

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[XuHuaiyu]

LGTM

[XuHuaiyu]

/merge

[ti-chi-bot]

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

Commit hash: f23883e

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