fix: referential equalities should ignore child nodes

[KATT]

Closes #245

• Short-circuit result of the walker on already-seen objects
• Will make outputs less noisy
• Should make superjson faster too

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yarn test --watch --testNamePattern "#245" --testPathPattern index

[Skn0tt]

Published as part of https://github.com/blitz-js/superjson/releases/tag/v1.13.0