import: fix memory leak (#39332)

[ti-chi-bot]

This is an automated cherry-pick of #39332

What problem does this PR solve?

Issue Number: close #39331

Problem Summary:

What is changed and how it works?

When kvMemBuf reuses the byte buffer in the available byte buffer pool, iterate on all the byte buffer's capacity. If it can find at least one byte buffer with a large capacity, it will choose to reuse it, rather than create a new byte buffer.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
  compile the modified version, and check whether memory leak has been fixed. Here are the heap profiles of the Lightning process after the modification:
  
• 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 been approved by:

• dsdashun
• lance6716

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.

[dsdashun]

/run-unit-test

[dsdashun]

/run-unit-test

[dsdashun]

/run-integration-br-test

[dsdashun]

/cc @lance6716 @D3Hunter

[dsdashun]

/merge

[ti-chi-bot]

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

Commit hash: 5472b00

[ti-chi-bot]

@ti-chi-bot: Your PR was out of date, I have automatically updated it for you.

If the CI test fails, you just re-trigger the test that failed and the bot will merge the PR for you after the CI passes.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the ti-community-infra/tichi repository.