Fix the latest version when merging top n results

[peachisai]

• If this pull request closes/resolves/fixes an existing issue, replace the issue number. Fixes apache/skywalking#.
• Update the CHANGES log.

[wu-sheng]

Please update changes if this bug exists from 0.9.

[Copilot]

Pull request overview

This pull request fixes a bug in the version handling when merging top N results in BanyanDB's measure query logic.

Changes:

• Refactored hardcoded schema name to use constant for better maintainability
• Fixed version update logic to execute outside the field columns loop, ensuring proper version tracking

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
banyand/measure/query.go	Replaced hardcoded string "_top_n_result" with TopNSchemaName constant
banyand/measure/block.go	Moved version update logic outside the for loop to ensure it executes once per merge operation

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[codecov-commenter]

Codecov Report

❌ Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 47.17%. Comparing base (3530dd9) to head (4f90e91).
⚠️ Report is 122 commits behind head on main.

Files with missing lines	Patch %	Lines
banyand/measure/query.go	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #958      +/-   ##
==========================================
+ Coverage   45.97%   47.17%   +1.19%     
==========================================
  Files         328      384      +56     
  Lines       55505    59626    +4121     
==========================================
+ Hits        25520    28128    +2608     
- Misses      27909    28867     +958     
- Partials     2076     2631     +555     

Flag	Coverage Δ
banyand	49.62% <50.00%> (?)
bydbctl	81.91% <ø> (?)
fodc	78.68% <ø> (?)
integration-distributed	80.00% <ø> (?)
pkg	29.32% <ø> (?)

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[peachisai]

Please update changes if this bug exists from 0.9.

Actually not ,it is related to #937