stmtsummary: change `plan_hint` column type to `text`

[henrybw]

What problem does this PR solve?

Issue Number: close #56057

Problem Summary: The plan_hint column type is currently a VARCHAR(64), but plan hints are not limited to 64 characters and may exceed this size. Normally this would raise a "Data Too Long" warning and truncate the column value, but due to #60330, internal memtable column values are not type checked.

What changed and how does it work?

Change the plan_hint column type to text instead.

Check List

Tests

• [x] Unit test
• [x] 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

[tiprow[bot]]

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[terry1purcell]

/ok-to-test

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 76.0309%. Comparing base (755cc34) to head (f020afb). Report is 479 commits behind head on master.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #60331        +/-   ##
================================================
+ Coverage   73.1169%   76.0309%   +2.9139%     
================================================
  Files          1710       1788        +78     
  Lines        472562     542366     +69804     
================================================
+ Hits         345523     412366     +66843     
- Misses       105763     106490       +727     
- Partials      21276      23510      +2234     

Flag	Coverage Δ
integration	53.6909% <ø> (?)
unit	72.9347% <ø> (+0.6275%)	:arrow_up:

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Components	Coverage Δ
dumpling	52.7804% <ø> (+0.0893%)	:arrow_up:
parser	∅ <ø> (∅)
br	66.0900% <ø> (+18.8559%)	:arrow_up:

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[bb7133]

Could you add a test case for this change?

[henrybw]

Could you add a test case for this change?

So this is a bit tricky to test right now, because currently this behavior doesn't generate an error for memtables (at least until https://github.com/pingcap/tidb/issues/60330 is fixed).

[ti-chi-bot[bot]]

[LGTM Timeline notifier]

Timeline:

• 2025-04-27 10:25:11.529381718 +0000 UTC m=+783255.341172097: :ballot_box_with_check: agreed by xhebox.
• 2025-06-17 08:53:29.821787235 +0000 UTC m=+175462.544966216: :ballot_box_with_check: agreed by qw4990.

[qw4990]

/retest

[ti-chi-bot[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: qw4990, tangenta, xhebox

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[henrybw]

/retest