types: print argument as hex literal if non-printable (#65384)

[ti-chi-bot]

This is an automated cherry-pick of #65384

What problem does this PR solve?

Issue Number: close #65383

Problem Summary:

What changed and how does it work?

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.

Non printable arguments for prepared statements are now printed in hex in the slow query log

Alternatives

1. Looping over the string and checking for < 0x20 (non printable ASCII and 0x7f (DEL). However that doesn't check any multi-byte non-BMP runes (e.g. \u2060 (SWJ).
2. Using datum.GetStringWithCheck(). Probably heavier and might only check if a string is valid, not if it is printable as well.

[ti-chi-bot]

@dveeden This PR has conflicts, I have hold it.
Please resolve them or ask others to resolve them, then comment /unhold to remove the hold label.

[ti-chi-bot]

@ti-chi-bot: ## If you want to know how to resolve it, please read the guide in TiDB Dev Guide.

Details

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
⚠️ Please upload report for BASE (release-8.5@8e7f3fe). Learn more about missing BASE report.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-8.5     #65510   +/-   ##
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  Coverage               ?   71.1183%           
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  Files                  ?       1681           
  Lines                  ?     469228           
  Branches               ?          0           
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  Hits                   ?     333707           
  Misses                 ?     113739           
  Partials               ?      21782           

Flag	Coverage Δ
integration	46.6680% <61.5384%> (?)
unit	64.8783% <100.0000%> (?)

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

Components	Coverage Δ
dumpling	52.9278% <0.0000%> (?)
parser	∅ <0.0000%> (?)
br	40.3916% <0.0000%> (?)

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[dveeden]

/unhold

[dveeden]

/retest

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: qw4990
Once this PR has been reviewed and has the lgtm label, please assign benmeadowcroft 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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Details

Needs approval from an approver in each of these files:

• OWNERS [qw4990]
• pkg/sessionctx/variable/OWNERS

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2026-01-14 01:08:26.822256645 +0000 UTC m=+406150.884121554: ☑️ agreed by qw4990.