fix: preserve custom layout falsy values

[biubiukam]

This is a ...

• New feature
• Bug fix
• TypeScript definition update
• Bundle size optimization
• Performance optimization
• Enhancement feature
• Refactoring
• Update dependency
• Code style optimization
• Test Case
• Branch merge
• Site / documentation update
• Demo update
• Workflow
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• Release
• Other (about what?)

Related issue link

close #1949

Background and solution

Custom layout and custom render callbacks used table.getCellValue(...) || '' for the callback value. That converted valid falsy cell values such as 0 and false into an empty string, so custom layout logic could not distinguish those values from an empty cell.

This change passes table.getCellValue(...) through directly for custom layout and custom render callback args, the custom width/height measurement paths, and React custom layout updates.

Changelog

Language	Changelog
English	Preserve falsy cell values for custom layout and custom render callbacks.
Chinese	自定义布局和自定义渲染回调中保留单元格的假值。

Self-Check before Merge

Please check all items below before requesting a reviewing.

• Doc is updated/provided or not needed
• Demo is updated/provided or not needed
• TypeScript definition is updated/provided or not needed
• Changelog is provided or not needed

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Summary

• Preserve 0 and false cell values in custom layout and custom render callback args.
• Apply the same value passthrough during custom width/height computation and React custom layout updates.
• Add a regression test for custom layout callback args.

Walkthrough

• Added a custom layout test covering 0 and false callback values.
• Removed the empty-string fallback from custom layout and custom render value plumbing.

Validation

• node ../../common/scripts/install-run-rushx.js test -- columns/listTable-custom-layout.test.ts --runInBand
• node common/scripts/install-run-rush.js build -t @visactor/react-vtable
• node common/scripts/install-run-rush.js build -t @visactor/vtable-sheet
• git push -u origin fix/issue-1949-custom-layout-value