Add Support for Standard Schema

[Tyler-Petrov]

This PR adds support for using any Standard Schema schema for validation. The validation.zod options is deprecated now in favor of validation.schema. I tried to keep all other functionality exactly the same.

[harryhdt]

Hi @Tyler-Petrov — thanks a lot for the contribution!
I really appreciate the effort.

However, for the next release I’m planning to move the validation system in a more generic direction. This means removing all built-in validation helpers (including the Zod-specific one) so users can plug in whatever validator they prefer — Zod, Valibot, custom logic, anything.

Because of that, I’m not planning to introduce new built-in schema options right now.

Thanks again for taking the time to help improve the library, and I hope you stick around for the upcoming version! 🙌