optimize: fix go vet issue

[slievrly]

What this PR does:

Which issue(s) this PR fixes:

Fixes #889

go vet ./...

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 38.17%. Comparing base (f6da25c) to head (9f1d83f).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #892   +/-   ##
=======================================
  Coverage   38.17%   38.17%           
=======================================
  Files         188      188           
  Lines       11417    11417           
=======================================
  Hits         4359     4359           
  Misses       6628     6628           
  Partials      430      430           

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[Copilot]

Pull Request Overview

This PR fixes Go vet issues by correcting struct literal syntax and removing unused fields. The changes ensure the code follows proper Go conventions and passes static analysis checks.

• Fixed struct literal initializations to use named field syntax
• Removed unused lock field from test structs
• Updated test cases to use proper Go struct initialization patterns

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
pkg/datasource/sql/undo/builder/basic_undo_log_builder_test.go	Fixed RowImage struct literals to use named Columns field
pkg/datasource/sql/exec/at/base_executor_test.go	Fixed RowImage struct literals to use named Columns field
pkg/datasource/sql/datasource/base/meta_cache_test.go	Removed unused lock field from test struct definitions

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