Add TypeScript types for api

**Description**
Currently lib lacks proper serialization support.

**Proposed solution**
Add configurable serialization with sensible defaults.

**Priority**: Low/Medium

Start by locating the API implementation and the relevant files under lib, then determine where serialization is currently handled or missing. Define the TypeScript API types and configurable serialization defaults described in the issue, and verify that the resulting behavior is covered by the repository's existing checks.

Written by the indexing model from the issue text.