feat: add hybrid cjs-esm support

[Nesopie]

• We discussed this in the stream but are you happy with the way tests are being done right now? Currently they're being run from the source itself. This prevents build files from getting into the bundle but I can revert to testing both of them individually as well.

• TODO: Have to change the other commands as well apart from build and test

[Nesopie]

I've tested out the other commands and they work fine too, @junderw can you have a look?

[junderw]

Could you convert the existing travis CI config to Github Actions CI so I can run the tests and lints on this? Thanks.

[Nesopie]

Hey! The devDependency I used to run ts files, i.e. tsx is not supported on lower versions of node so tests start failing on those versions (passes on lts) in the CI.

I've tried instead to run tests on two different builds without tsx but that requires you to change the way imports are done on both the files (which can't be done as they're built from the same source so you can't get two different outputs).

One suggestion would be to just test on one build and stick with that, however I'd like your opinion on this before I move ahead

[junderw]

Testing one build should be fine