Provide ESM build output

As the ecosystem moves towards ESM support by default, this package should too.

This will be a breaking change.

https://blog.sindresorhus.com/hello-modules-d1010b4e777b

Note: some dependencies are not yet ready:
- Jest - https://jestjs.io/docs/ecmascript-modules

Check the project's build configuration (likely in package.json or a build tool like tsup/rollup). Understand current CommonJS output and how to add ESM output, which may involve dual package publishing. Review linked article for migration context. Note that Jest dependency is not ESM-ready, so testing may be affected. Verify if other dependencies support ESM.

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