Handle dual queries with LIMIT on the vtgate

[systay]

Description

Dual queries can most of the time be handled on the vtgate side, without having to send anything down to MySQL.

This PR extends this functionality to include dual queries with LIMIT in them.

Checklist

• "Backport to:" labels have been added if this change should be back-ported to release branches
• If this change is to be back-ported to previous releases, a justification is included in the PR description
• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on CI?
• Documentation was added or is not required

[vitess-bot]

Review Checklist

Hello reviewers! 👋 Please follow this checklist when reviewing this Pull Request.

General

• Ensure that the Pull Request has a descriptive title.
• Ensure there is a link to an issue (except for internal cleanup and flaky test fixes), new features should have an RFC that documents use cases and test cases.

Tests

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Documentation

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• There should be a comment at the top of each new or modified test to explain what the test does.

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Backward compatibility

• Protobuf changes should be wire-compatible.
• Changes to _vt tables and RPCs need to be backward compatible.
• RPC changes should be compatible with vitess-operator
• If a flag is removed, then it should also be removed from vitess-operator and arewefastyet, if used there.
• vtctl command output order should be stable and awk-able.

[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 68.68%. Comparing base (66bf89b) to head (50db00a).
Report is 2 commits behind head on main.

Files	Patch %	Lines
go/vt/vtgate/planbuilder/select.go	75.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16400      +/-   ##
==========================================
+ Coverage   68.66%   68.68%   +0.02%     
==========================================
  Files        1548     1548              
  Lines      199084   199098      +14     
==========================================
+ Hits       136699   136751      +52     
+ Misses      62385    62347      -38     

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