Native ESM

[smorimoto]

I propose here to update the codebase to the native ESM.

For better ESM support in something like Remix, updating the codebase to ESM and running builds for ESM and CJS using things like tsup will, in my opinion, give library developers and library users the best DX at the moment.

I've been working on that in our internal packages for the last few months, so if we can get an consensus, I'd be happy to do that here as well!

[smorimoto]

The biggest theme of the propose is trying to get "true" ESM package publishing compatibility in place, while still supporting CJS in the published package. (In this chaotic JS ecosystem, we have Faux ESM and native ESM...)