Feature request: add commonjs and esm exports

[ericallam]

Currently superjson does not export commonjs, only ESM. It would be great to support both formats. Our package that we use superjson in supports both formats and having superjson be ESM only causes some issues. It's really easy these days to create a dual-package using something like tshy (which is what we use). If you are open to it, I'd be happy to create a PR.