Add TypeScript typings for query objects

[ak-pm]

Hi 👋

Thank you for maintaining this helpful library!

I’m currently using json-to-graphql-query in a TypeScript project and found it very useful. However, the lack of TypeScript types makes integration a bit harder. I’ve started working on typings by forking the repo and would like to contribute back by opening a PR.

My goals are:

• Add TypeScript definitions for the public API (e.g. jsonToGraphQLQuery, config options, etc.)
• Ensure the library remains backward compatible for existing JavaScript users
• Add type tests if needed

Would you be open to reviewing and merging such a contribution?

If there's anything specific you'd like me to consider while preparing the PR (project structure, testing, code style), please let me know.

Thanks!