Add "exports" section to package.json

[brandoncharnesky]

Add an "exports" section to the package.json to define the cjs/esm versions (https://nodejs.org/api/packages.html#conditional-exports). Some downstream tools (vitest: https://github.com./vitest-dev/vitest/discussions/4233) fail to recognize the current method we are using (defining "module" in the package.json file).

Unclear if there would be other downstream effects from adding in this "exports" section.