expression: Truncate long strings in EXPLAIN

[EricZequan]

What problem does this PR solve?

Issue Number: ref #54245

Problem Summary:
When used with prepared statement, there will be a CAST(String, Vector) in the plan. Previously, we did not correctly truncate long strings. This result in very large slow log when there are vector queries.

What changed and how does it work?

Truncate long strings, so that in vector query scenarios logs will not bloat too much.

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]

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[tiprow]

Hi @EricZequan. Thanks for your PR.

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[codecov]

Codecov Report

Attention: Patch coverage is 89.83051% with 6 lines in your changes missing coverage. Please review.

Please upload report for BASE (feature/vector-search/vector-data-type@573e1ab). Learn more about missing BASE report.

Additional details and impacted files

@@                             Coverage Diff                             @@
##             feature/vector-search/vector-data-type     #55412   +/-   ##
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  Coverage                                          ?   74.4089%           
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  Files                                             ?       1561           
  Lines                                             ?     440170           
  Branches                                          ?          0           
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  Hits                                              ?     327526           
  Misses                                            ?      92369           
  Partials                                          ?      20275           

Flag	Coverage Δ
integration	47.8763% <10.1694%> (?)

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Components	Coverage Δ
dumpling	52.9656% <0.0000%> (?)
parser	∅ <0.0000%> (?)
br	52.4687% <0.0000%> (?)

[ti-chi-bot]

@EricZequan: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
idc-jenkins-ci-tidb/check_dev_2	e2701e7	link	true	/test check-dev2
idc-jenkins-ci-tidb/unit-test	e2701e7	link	true	/test unit-test

Full PR test history. Your PR dashboard.

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[breezewish]

Close for #55934