Docs: Update security usage example by moving away from third party library

[JacobCoffee]

We'd have to handle the type coercion that case, but I think better to use either msgspec and convert() if we don't want to roll the type parsing ourselves, or dataclasses.

(I only say prefer msgspec over pydantic b/c its available without another dependency).

Originally posted by @peterschutt in #3344 (comment)

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