client/tso: fix the issue where the TSO follower proxy cannot be closed

[JmPotato]

What problem does this PR solve?

Issue Number: close #8709.

What is changed and how does it work?

Remove outdated follower connections after disabling the TSO follower proxy.

Check List

Tests

• Unit test
• Integration test

Release note

Fix the issue where the TSO follower proxy cannot be closed.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 71.73%. Comparing base (48e72f1) to head (327a599).
Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8719      +/-   ##
==========================================
+ Coverage   71.70%   71.73%   +0.02%     
==========================================
  Files         517      517              
  Lines       67450    67456       +6     
==========================================
+ Hits        48364    48388      +24     
+ Misses      15521    15507      -14     
+ Partials     3565     3561       -4     

Flag	Coverage Δ
unittests	71.73% <100.00%> (+0.02%)	⬆️

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

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: lhy1024, nolouch

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Needs approval from an approver in each of these files:

• OWNERS [lhy1024,nolouch]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-10-16 04:12:37.856078529 +0000 UTC m=+417155.004988353: ☑️ agreed by nolouch.
• 2024-10-16 06:45:59.249218077 +0000 UTC m=+426356.398127909: ☑️ agreed by lhy1024.

[JmPotato]

/cherry-pick release-8.4

[ti-chi-bot]

@JmPotato: new pull request created to branch release-8.4: #8721.

In response to this:

/cherry-pick release-8.4

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