Remove unnecessary duplicate type definitions (TS interfaces and Zod schemas)

[glevco]

PR #728 introduced support for bigint output values, and it uses Zod schemas. Zod has a tool (infer) to generate TypeScript types based on schema definitions (but not the other way around).

For now, we have duplicate type definitions: our previously defined TS interfaces, and the equivalent Zod schema (example). We do verify that they match, but instead we could simply remove the TS interfaces and use Zod.infer to generate the types.

• Remove duplicate type definitions
• Review naming (feat: implement bigint support #728 (comment))