Add ESM/CJS import tests

[sangaline]

This adds some basic tests to make sure that the ESM and CJS builds are working. It's easy to accidentally add a library that doesn't work with one of the builds, or to do something that pushes the library under a default property on the CJS build. I've added and reverted a few commits here that demonstrate these issues and the tests catching them.

In particular, see these commits which introduce different errors:

• a182acf - Introduce an ESM-only dependency
• 019fd03 - Force the CJS build to export the library under .default
• 495f335 - Use a CJS only library as an ESM import

Closes #63

[katiemckeon]

Appreciate the visibility into this.

My main exposure to the CJS vs ESM problem is one where I clone a codebase that does nearly what I want (e.g. a snarkjs app or tiny-noir-js demo website) and revise commands to show how you can easily export proof requests via our SDK. Honestly I'm pretty lost on the finer comparison between the two, but I appreciate that we are making it a priority to support both.