fix(vtable-sheet): exclude test shim from compile

[dajiaohuang]

🤔 This is a ...

• Bug fix
• TypeScript definition update

🔗 Related issue link

Fixes #5295

💡 Background and solution

vtable-sheet's production TypeScript project currently includes src/test-shims/vtable-plugins.ts. That test-only shim re-exports the sibling vtable-plugins source tree, which is outside vtable-sheet's configured rootDir, so rushx compile fails with TS6059/TS6307 diagnostics.

This change:

• excludes the test-only shim directory from the production tsconfig; and
• imports MultiSheetImportResult from the existing public @visactor/vtable-plugins export instead of its source path.

The Jest configuration continues to resolve the shim for package tests.

📝 Changelog

Language	Changelog
🇺🇸 English	Keep test-only plugin sources out of the vtable-sheet production compile.
🇨🇳 Chinese	避免 vtable-sheet 生产编译包含仅测试使用的插件源码。

☑️ Self-Check before Merge

• 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

Testing

• node ../../common/scripts/install-run-rushx.js compile in packages/vtable-sheet
• node ../../common/scripts/install-run-rushx.js test in packages/vtable-sheet (76 suites, 446 tests)
• Repository pre-push hook: rush test --only tag:package
• rush build -t @visactor/vtable-sheet (completed with the repository's existing warning-tolerant build configuration)