fix(langchain/zod): Support optionals in zod transform interop

[ro0sterjam]

interopZodTransformInputSchema currently does not remove transform functions from schemas nested under and optional. This PR fixes that.

Fixes #9120

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[christian-bromann]

Really appreciate you taking the time to open this PR, @ro0sterjam 🙏
The team is currently focused on shipping our v1 release, so we’re pausing detailed reviews for a bit. We’ll follow up within the next 2–4 weeks once things settle — thanks so much for your patience!