tablecodec: fix the issue that decoding an index value might panic (#53034)

[ti-chi-bot]

This is an automated cherry-pick of #53034

What problem does this PR solve?

Issue Number: close #47115

Problem Summary: decoding an index value with large padding size might panic, because the padding size is:

• encoded via: types.NewUintDatum(paddingSize) => encodeUint
• decoded via decodeRestoredValuesV5 => rd.DecodeToBytesNoHandle => rd.encodeOldDatum(IntFlag) => codec.EncodeVarint(buf, decodeInt(raw)) because the field type is not marked as unsigned in buildRestoredColumn.

What changed and how does it work?

Set unsigned flag to the field type correctly.

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

All modified and coverable lines are covered by tests ✅

❗ No coverage uploaded for pull request base (release-6.5@389b0c1). Click here to learn what that means.

Additional details and impacted files

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[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: crazycs520, ekexium

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-05-11 04:23:49.158809202 +0000 UTC m=+1281582.915944823: ☑️ agreed by crazycs520.
• 2024-05-13 01:59:13.853997032 +0000 UTC m=+1445707.611132607: ☑️ agreed by ekexium.