br: cancel context when timer stop (#56948)

[ti-chi-bot]

This is an automated cherry-pick of #56948

What problem does this PR solve?

Issue Number: ref #53480

Problem Summary:
the context will leak because it is not cancelled.

What changed and how does it work?

cancel the context

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 APPROVED

This pull-request has been approved by: 3pointer, Leavrth

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Needs approval from an approver in each of these files:

• br/OWNERS [3pointer,Leavrth]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-10-31 06:03:42.170097317 +0000 UTC m=+502535.009252857: ☑️ agreed by Leavrth.
• 2024-10-31 06:04:25.719346936 +0000 UTC m=+502578.558502479: ☑️ agreed by 3pointer.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Please upload report for BASE (release-7.5@f54a797). Learn more about missing BASE report.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-7.5     #57009   +/-   ##
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  Coverage               ?   72.0178%           
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  Files                  ?       1415           
  Lines                  ?     412609           
  Branches               ?          0           
================================================
  Hits                   ?     297152           
  Misses                 ?      95547           
  Partials               ?      19910           

Flag	Coverage Δ
unit	72.0178% <100.0000%> (?)

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

Components	Coverage Δ
dumpling	52.9400% <0.0000%> (?)
parser	∅ <0.0000%> (?)
br	53.5345% <0.0000%> (?)