Export o1js testing framework

[boray]

Export testing utilities from src/lib/testing to the npm package to enable their use by third party library developers.

[Trivo25]

see #1677

[45930]

What will be the dependency tree between o1js, the o1js-testing-utils package, and some third party package that uses both?

[45930]

@Trivo25 it's not clear if #1677 is meant for internal or external devs

[Trivo25]

@45930 this should eventually be made available to external developers

[45930]

Got it. Are you opposed to exporting a simple version to developers now and eventually making it better, rather than the inverse?

Specifically, we would like to use it in a library we are building. The alternative is to just put more code into o1js that doesn't have to be there, but if we could get the tools we want to use out faster, we could start adding more things as libraries as well.