go/mysql: use clear builtin for zerofill

[mattrobenolt]

This is implemented as the same performance optimization, but is a more clear intention.

Related issues:

Part of #16789
Iteration from #16341

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

• Bug fixes should have at least one unit or end-to-end test, enhancement and new features should have a sufficient number of tests.

Documentation

• Apply the release notes (needs details) label if users need to know about this change.
• New features should be documented.
• There should be some code comments as to why things are implemented the way they are.
• There should be a comment at the top of each new or modified test to explain what the test does.

New flags

• Is this flag really necessary?
• Flag names must be clear and intuitive, use dashes (-), and have a clear help text.

If a workflow is added or modified:

• Each item in Jobs should be named in order to mark it as required.
• If the workflow needs to be marked as required, the maintainer team must be notified.

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

All modified and coverable lines are covered by tests ✅

Project coverage is 68.71%. Comparing base (0db3577) to head (e09e773).
Report is 6 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #16348   +/-   ##
=======================================
  Coverage   68.71%   68.71%           
=======================================
  Files        1547     1547           
  Lines      198287   198285    -2     
=======================================
+ Hits       136243   136250    +7     
+ Misses      62044    62035    -9     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[mattlord]

// The clear built-in function clears maps and slices.
// For maps, clear deletes all entries, resulting in an empty map.
// For slices, clear sets all elements up to the length of the slice
// to the zero value of the respective element type. If the argument
// type is a type parameter, the type parameter's type set must
// contain only map or slice types, and clear performs the operation
// implied by the type argument.
func clear[T ~[]Type | ~map[Type]Type1](t T)

👍 Thanks, @mattrobenolt !