*: merge the runtime stats in time to avoid using too many memory (#39394)

[ti-chi-bot]

This is an automated cherry-pick of #39394

What problem does this PR solve?

Issue Number: close #39413

Now tidb need to record some runtime stats for each executor/cop_task and so on, and merge them after the sql finfished.
If there are many cop tasks, the memory can't gc and hold util the sql finfished. Maybe it cause OOM.

Problem Summary:

When the stats will not updated, merge it to the summary stats.

What is changed and how it works?

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

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

None

[ti-chi-bot]

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[ti-chi-bot]

@ti-chi-bot: This cherry pick PR is for a release branch and has not yet been approved by release team.
Adding the do-not-merge/cherry-pick-not-approved label.

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AFTER it has been approved by collaborators, please ping the release team in a comment to request a cherry pick review.

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