br: handle the merged SST response

[Leavrth]

What problem does this PR solve?

Issue Number: close #57389

Problem Summary:
the backup merge data from different key ranges into one SST file, so BR needs to be able to handle its response.

What changed and how does it work?

handle the merged SST response.

Check List

Tests

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

  • I checked and no code files have been changed.

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]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[tiprow]

Hi @Leavrth. Thanks for your PR.

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.4736%. Comparing base (7e659e4) to head (ae85026).

❗ Current head ae85026 differs from pull request most recent head 160061e

Please upload reports for the commit 160061e to get more accurate results.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #57576        +/-   ##
================================================
- Coverage   73.5202%   73.4736%   -0.0467%     
================================================
  Files          1681       1705        +24     
  Lines        464348     469771      +5423     
================================================
+ Hits         341390     345158      +3768     
- Misses       102121     103145      +1024     
- Partials      20837      21468       +631     

Flag	Coverage Δ
integration	52.9761% <ø> (?)

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

Components	Coverage Δ
dumpling	52.6910% <ø> (ø)
parser	∅ <ø> (∅)
br	45.9522% <ø> (+0.1807%)	⬆️

[ti-chi-bot]

@Leavrth: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
idc-jenkins-ci-tidb/check_dev	160061e	link	true	/test check-dev
idc-jenkins-ci-tidb/check_dev_2	160061e	link	true	/test check-dev2
idc-jenkins-ci-tidb/build	160061e	link	true	/test build
idc-jenkins-ci-tidb/unit-test	160061e	link	true	/test unit-test
pull-br-integration-test	160061e	link	true	/test pull-br-integration-test
pull-integration-ddl-test	160061e	link	true	/test pull-integration-ddl-test
pull-integration-e2e-test	160061e	link	true	/test pull-integration-e2e-test
pull-mysql-client-test	160061e	link	true	/test pull-mysql-client-test
idc-jenkins-ci-tidb/mysql-test	160061e	link	true	/test mysql-test
pull-lightning-integration-test	160061e	link	true	/test pull-lightning-integration-test

Full PR test history. Your PR dashboard.

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