In-memory engine: add metrics for range count

[SpadeA-Tang]

What is changed and how it works?

Issue Number: Ref #16141

What's Changed:

add metrics for range count

It shows the different types of range count:

Related changes

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

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Release note

None

[ti-chi-bot]

[REVIEW NOTIFICATION]

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• LykxSassinator
• tonyxuqqi

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[SpadeA-Tang]

/merge

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[ti-chi-bot]

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

Commit hash: fae27c4

[SpadeA-Tang]

/retest-required