test: add yjs suite + fast gate

[zbeyens]

Summary

• add fast Yjs coverage for plugin init/api, provider wrappers, registry, composition, and deterministic state seeding
• add opt-in Yjs collaboration slow tests behind pnpm test:slow
• gate the fast lane with pnpm test:slowest, keep pnpm test:profile as the non-failing profiler, and ignore bulky coverage TSV artifacts

Verification

• pnpm lint:fix
• pnpm test:profile -- --top 5 packages/yjs/src
• pnpm test:slowest -- --top 5 packages/yjs/src
• pnpm check

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Latest commit: 5f5b748

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Project	Deployment	Actions	Updated (UTC)
plate	Ready	Preview, Comment	Mar 22, 2026 2:15pm