planner: use slices.Sort to simple code

[hawkingrei]

What problem does this PR solve?

Issue Number: close #xxx

Problem Summary:

What changed and how does it work?

use slices.Sort to simple code

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 ✅

Project coverage is 73.5463%. Comparing base (f4989a6) to head (bed5064).
Report is 2 commits behind head on master.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #61505        +/-   ##
================================================
+ Coverage   73.0972%   73.5463%   +0.4490%     
================================================
  Files          1729       1729                
  Lines        480683     480697        +14     
================================================
+ Hits         351366     353535      +2169     
+ Misses       107765     105631      -2134     
+ Partials      21552      21531        -21     

Flag	Coverage Δ
integration	42.4314% <100.0000%> (?)
unit	72.4182% <100.0000%> (+0.0558%)	⬆️

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

Components	Coverage Δ
dumpling	52.7804% <ø> (ø)
parser	∅ <ø> (∅)
br	46.9629% <ø> (-0.0053%)	⬇️

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[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: lance6716, qw4990

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• pkg/planner/OWNERS [qw4990]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-06-05 04:02:04.772851882 +0000 UTC m=+500810.975197147: ☑️ agreed by qw4990.
• 2025-06-05 04:58:03.174300593 +0000 UTC m=+504169.376645858: ☑️ agreed by lance6716.