*: 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]

[REVIEW NOTIFICATION]

This pull request has not been approved.

To complete the pull request process, please ask the reviewers in the list to review by filling /cc @reviewer in the comment.
After your PR has acquired the required number of LGTMs, you can assign this pull request to the committer in the list by filling /assign @committer in the comment to help you merge this pull request.

The full list of commands accepted by this bot can be found here.

Reviewer can indicate their review by submitting an approval review.
Reviewer can cancel approval by submitting a request changes review.