client: signal RG GC goroutines to exit properly

[yzhan1]

What problem does this PR solve?

Issue Number: Close #9745

What is changed and how does it work?

Adds a new cancel channel to signal GC goroutines when they can be stopped, to prevent goroutine leaks on client side.

client: signal RG GC goroutines to exit properly

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below) Manually tested using TiDB build with the same traffic which generates 600 extra goroutines stuck in handleTokenBucketUpdateEvent. After the fix only 1 goroutine in handleTokenBucketUpdateEvent.
• No code

Code changes

• Has the configuration change
• Has HTTP API interfaces changed (Don't forget to add the declarative for the new API)
• Has persistent data change

Side effects

• Possible performance regression
• Increased code complexity
• Breaking backward compatibility

Related changes

• PR to update pingcap/docs/pingcap/docs-cn:
• PR to update pingcap/tiup:
• Need to cherry-pick to the release branch

Release note

None.

[ti-chi-bot[bot]]

Hi @yzhan1. Thanks for your PR.

I'm waiting for a tikv member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[yzhan1]

@okJiang @JmPotato updated based on comments. PTAL, thanks!

[ti-chi-bot[bot]]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: okJiang Once this PR has been reviewed and has the lgtm label, please assign disksing for approval. For more information see the Code Review Process. Please ensure that each of them provides their approval before proceeding.

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[ti-chi-bot[bot]]

[LGTM Timeline notifier]

Timeline:

• 2025-09-25 02:53:07.960048019 +0000 UTC m=+497998.030541694: :ballot_box_with_check: agreed by okJiang.

[okJiang]

/retest

[codecov[bot]]

Codecov Report

:x: Patch coverage is 66.66667% with 6 lines in your changes missing coverage. Please review. :white_check_mark: Project coverage is 76.90%. Comparing base (53b1fbf) to head (5754471). :warning: Report is 26 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #9749      +/-   ##
==========================================
+ Coverage   76.84%   76.90%   +0.05%     
==========================================
  Files         484      486       +2     
  Lines       77142    77411     +269     
==========================================
+ Hits        59281    59534     +253     
- Misses      14258    14261       +3     
- Partials     3603     3616      +13     

Flag	Coverage Δ
unittests	76.90% <66.66%> (+0.05%)	:arrow_up:

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[okJiang]

/cc @JmPotato @bufferflies