sink(ticdc): add batch buffer for flush worker

[Rustin170506]

What problem does this PR solve?

Issue Number: ref #4423

What is changed and how it works?

add batch buffer for flush worker. Avoid frequent memory allocation here.

Check List

Tests

• Unit test

Code changes

None

Side effects

None

Related changes

None

Release note

None

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• overvenus
• sdojjy

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[Rustin170506]

/merge

[ti-chi-bot]

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

Commit hash: bca7121

[Rustin170506]

/run-verify

[codecov-commenter]

Codecov Report

Merging #4884 (c210381) into master (687e248) will increase coverage by 0.1761%.
The diff coverage is 58.5421%.

❗ Current head c210381 differs from pull request most recent head 5c069f9. Consider uploading reports for the commit 5c069f9 to get more accurate results

Flag	Coverage Δ
cdc	60.9722% <59.1240%> (+0.3736%)	⬆️
dm	52.4596% <50.0000%> (-0.0100%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

@@               Coverage Diff                @@
##             master      #4884        +/-   ##
================================================
+ Coverage   56.1240%   56.3001%   +0.1761%     
================================================
  Files           522        524         +2     
  Lines         65325      65522       +197     
================================================
+ Hits          36663      36889       +226     
+ Misses        25094      25031        -63     
- Partials       3568       3602        +34     

[Rustin170506]

/run-kafka-integration-test

[ti-chi-bot]

@hi-rustin: Your PR was out of date, I have automatically updated it for you.

At the same time I will also trigger all tests for you:

/run-all-tests

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.

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[Rustin170506]

/run-kafka-integration-test
/run-verify

[overvenus]

/run-verify