client/tso: use the TSO request pool at the tsoClient level to avoid data race (#8077)

[ti-chi-bot]

This is an automated cherry-pick of #8077

What problem does this PR solve?

Issue Number: close #8055, ref #8076.

What is changed and how does it work?

Use the TSO request pool at the `tsoClient` level to avoid data race.

Check List

Tests

• Unit test
• Integration test

Release note

None.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• JmPotato
• rleungx

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[JmPotato]

/merge

[ti-chi-bot]

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/run-all-tests

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[ti-chi-bot]

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

Commit hash: 39b4e34