Provide esm version

With more and more build tools (vite, nuxt, etc) going towards an esm-first build, it would be nice if a proper [esm interface](https://nodejs.org/api/esm.html) could be provided, i.e. transpile and distribute esm version, including correct [export](https://nodejs.org/api/packages.html#conditional-exports) declaration in `package.json`.

Start by inspecting package.json and the repository's TypeScript build and distribution setup. Compare the current package exports with Node's ESM and conditional-exports guidance; done means a transpiled ESM distribution is published with correct package.json declarations and works with build tools such as Vite and Nuxt.

Written by the indexing model from the issue text.