test: cover Suspense retries in React streaming SSR

[aose-yuu]

Purpose

Extend the React adapter SSR test coverage so streaming Suspense retries cannot regress molecule cleanup behavior.

Summary

• Add streaming SSR Suspense retry coverage for useMolecule using a React.use()-based fixture.
• Verify renderToPipeableStream keeps suspended molecules undisposed at shell time and disposes every server-created instance after retries finish.
• Verify renderToReadableStream also disposes every retry-created molecule instance and keeps mount-time work disabled on the server.
• Leave the runtime and public API unchanged, and treat this as a test-only guardrail update.

Verification

• mise run ci