test: guard lazy segmenter package boundaries

[Justineo]

Summary

Follow-up to #127.

• Guard importing a freshly built root entry without Intl.Segmenter in an isolated process.
• Verify production Vite/Rolldown consumers remove segmentation for WrapClamp while retaining it for LineClamp.
• Correct the guarantee: unit-safe grapheme preparation skips segmentation, but ASCII word boundaries still require the native API. No Unicode fallback or public API change.

Design

• Build temporary artifacts independently of the workspace dist; the checks run in the existing test suite.
• Both regressions fail when eager construction is restored, and the text-consumer control prevents an empty bundle from passing.

[pkg-pr-new]

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npm i https://pkg.pr.new/vue-clamp@136

commit: 49f4674