planner: Fix vector not truncated after CBO (#58809)

[ti-chi-bot]

This is an automated cherry-pick of #58809

What problem does this PR solve?

Issue Number: Close #58837

Problem Summary:

What changed and how does it work?

After CBO is introduced, vector is not truncated in explain. This is what it looks like now without this PR:

Upstream PR: https://github.com/tidbcloud/tidb-cse/pull/1416

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

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Please upload report for BASE (release-8.5@0005334). Learn more about missing BASE report.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-8.5     #58844   +/-   ##
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  Coverage               ?   36.8100%           
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  Files                  ?       1675           
  Lines                  ?     611477           
  Branches               ?          0           
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  Hits                   ?     225085           
  Misses                 ?     364362           
  Partials               ?      22030           

Flag	Coverage Δ
integration	36.8100% <0.0000%> (?)

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

Components	Coverage Δ
dumpling	∅ <0.0000%> (?)
parser	∅ <0.0000%> (?)
br	23.2630% <0.0000%> (?)

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: AilinKid, XuHuaiyu

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Needs approval from an approver in each of these files:

• pkg/expression/OWNERS [XuHuaiyu]
• pkg/planner/OWNERS [AilinKid]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-01-10 03:26:08.204084695 +0000 UTC m=+496911.492916397: ☑️ agreed by XuHuaiyu.
• 2025-01-10 04:36:43.504126913 +0000 UTC m=+501146.792958620: ☑️ agreed by AilinKid.

[AilinKid]

seems it has conflicts